@article{xu_semenov_kim_2024, title={Voltage control of electromagnetic properties in antiferromagnetic materials}, volume={57}, ISSN={["1361-6463"]}, DOI={10.1088/1361-6463/ad3375}, abstractNote={Abstract}, number={24}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2024}, month={Jun} }
 @article{semenov_xu_boulton_kim_2023, title={Electrical control of Dzyaloshinskii-Moriya interactions in magnetic Weyl semimetals}, volume={108}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.108.134428}, abstractNote={The Dzyaloshinskii-Moriya interaction (DMI) is known to be responsible for multiple phenomena in magnetic materials. In the conventional description as a perturbation of the superexchange interaction by the spin-orbit coupling, the strength of the DMI is only weakly sensitive to the external fields, making its control difficult in spintronic applications. In this work, we show that an electrical modulation of the DMI may actually be possible in magnetic Weyl semimetals (WSMs). Specifically, it is theoretically illustrated that an antisymmetric indirect spin-spin interaction identified recently as an alternative mechanism for the DMI can result in the desired sensitivity to the external electric and magnetic fields via a redistribution of Weyl fermions among nodes of opposite chirality. This chiral anomaly enabled approach becomes particularly prominent in WSMs with inversion symmetry, in which the conventional DMI is not allowed. Numerical estimations suggest that moderate electric and magnetic fields of $\ensuremath{\sim}{10}^{3}--{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}$ and $\ensuremath{\sim}1$ T can induce a sufficiently strong change in the DMI. The impact of this externally modulated DMI on the manipulation of magnetic textures, including skyrmions in WSMs, is also discussed.}, number={13}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Xu, Xinyi and Boulton, James A. and Kim, Ki Wook}, year={2023}, month={Oct} }
 @article{semenov_kim_2023, title={Electrical control of antiferromagnetic domain walls in Weyl semimetals}, volume={107}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.107.094434}, abstractNote={The electric-field-induced angular force on the N\'eel vector in antiferromagnetic (AFM) Weyl semimetals (WSMs) is theoretically investigated. Unlike in the ferromagnetic (FM) counterparts, the magnetic textures in the AFM WSMs, such as the domain walls (DWs) appear to lack the torsion in the magnetization and, thus, unable to benefit from this highly efficient mechanism that originates from the axial magnetic effect. Contrarily, our calculations illustrate that the addition of the Dzyaloshinskii-Morya interaction can introduce a twist in the magnetization around the DW location, giving rise to a nonzero axial magnetic field. This axial magnetic field, when combined with an external electric field, can lead to an imbalance in the fermion density of Weyl cones of opposite chirality and, thus, a spatially localized net electron spin polarization. The resulting effective exchange field can exert an angular force on the AFM textures for spatial movement, which can be significant in certain AFM WSMs even under a moderate external electric field. The dynamics of the DW motion under this emergent angular force is analyzed by considering the balance of energy absorption and dissipation. Our investigation reveals the need to account for the contribution of the exchange dissipation mechanism beyond the typical Gilbert-like (relativistic) term to compensate the unusual superlinear rate of energy absorption by the AFM textures. The obtained DW velocity vs electric-field characteristics show a significant speedup for the N\'eel DWs in the AFM WSMs over the counterparts in the FM WSMs as well as those in the nontopological magnets. The analysis also elucidates the dependence of the DW motion on the DW chirality in these materials. Our results clearly indicate the significance of the energy-efficient axial magnetic effect in the dynamics of spin textures in AFM WSMs with broken inversion symmetry.}, number={9}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2023}, month={Mar} }
 @article{stephanovich_kirichenko_engel_semenov_kim_2021, title={Carrier-induced ferromagnetism in two-dimensional magnetically doped semiconductor structures}, volume={104}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.104.094423}, abstractNote={We show theoretically that the magnetic ions, randomly distributed in a two-dimensional (2D) semiconductor system, can generate a ferromagnetic long-range order via the RKKY interaction. The main physical reason is the discrete (rather than continuous) symmetry of the 2D Ising model of the spin-spin interaction mediated by the spin-orbit coupling of 2D free carriers, which precludes the validity of the Mermin-Wagner theorem. Further, the analysis clearly illustrates the crucial role of the molecular field fluctuations as opposed to the mean field. The developed theoretical model describes the desired magnetization and phase-transition temperature $T_c$ in terms of a single parameter; namely, the chemical potential $\mu$. Our results highlight a path way to reach the highest possible $T_c$ in a given material as well as an opportunity to control the magnetic properties externally (e.g., via a gate bias). Numerical estimations show that magnetic impurities such as Mn$^{2+}$ with spins $S=5/2$ can realize ferromagnetism with $T_c$ close to room temperature.}, number={9}, journal={PHYSICAL REVIEW B}, author={Stephanovich, V. A. and Kirichenko, E. and Engel, G. and Semenov, Yu G. and Kim, K. W.}, year={2021}, month={Sep} }
 @article{semenov_kim_2021, title={Spin-transfer and fieldlike torques in antiferromagnets}, volume={104}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.104.174402}, abstractNote={The phenomenon of spin-transfer torque (STT) in an antiferromagnet (AFM) is reexamined in terms of the incoming and outgoing spin currents. In contrast to the conventional approach, our model treats the STT as a result of the electron spin angular momentum transfer to the entire monodomain magnetic structure rather than to the individual sublattice magnetizations. This treatment enables the analysis to account for not only the destructive role of electron spin relaxation but also the potentially incomplete loss of electron spin phases that can either enhance the STT or suppress it depending on the structure parameters. Application of the developed model to the dynamical equation of the AFM order parameter illustrates the qualitative and quantitative differences with the conventional approach. Unlike the latter, our results predict a strong dependence of the STT on the orientation of the electron spin polarization relative to the magnetic anisotropy axes of the AFM. A similar characteristic also reveals a complex interplay in the N\'eel vector dynamics that can lead to a sublinear response of the oscillation frequency to the strength of the spin current. The impact of the fieldlike torque that can arise likewise from the spin injection is examined as well for a comprehensive account. The numerical calculations elucidate further the conditions that can elicit efficient manipulation of the magnetic states in an AFM under a spin-polarized current.}, number={17}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2021}, month={Nov} }
 @article{semenov_kim_2020, title={Efficient Control of Stochastic Switching via Spin Pumping in Antiferromagnetic Structures}, volume={13}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.13.064065}, abstractNote={Electrically controlled switching in an antiferromagnet (AFM), utilizing a currentless mechanism, is theoretically examined at finite temperatures. The structure consists of a metallic AFM with biaxial magnetic anisotropy sandwiched between a ferromagnetic spin filter and a semiconductor Schottky junction in a two-terminal pillar configuration. The calculations show that the torque necessary for the desired ${90}^{\ensuremath{\circ}}$ rotation of the N\'eel vector between two easy axes can be provided efficiently by pumping spin-polarized electrons into and out of the AFM through the metallic ferromagnetic layer. Consideration of thermal fluctuations illustrates the stochastic nature of the switching, whose probability distribution can be tailored by the electrical signal pulse as well as by the device dimensions. Detection of the N\'eel-vector state following this rotation may also be achieved straightforwardly via the large anisotropic magnetoresistance of the biaxial antiferromagnetic material. These properties, along with an ultrafast switching speed and a low energy requirement, are expected to be well suited for applications in nonvolatile memory and probabilistic computing.}, number={6}, journal={PHYSICAL REVIEW APPLIED}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Jun} }
 @article{regan_semenov_kim_2020, title={Optical bistability and self-opacity in magnetically doped monolayer transition metal dichalcogenides}, volume={102}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.102.214426}, abstractNote={Magneto-optical control of optical absorption spectra is theoretically investigated in two-dimensional (2D) dilute magnetic semiconductors such as monolayer transition metal dichalcogenides (TMDs) doped with magnetic ions. The underlying mechanism relies on efficient spin transfer between spin-polarized photoexcited carriers and localized magnetic ions via exchange scattering, and subsequent shifts in the electronic band structure induced by the resulting time-reversal symmetry breaking. A self-consistent model based on a rate equation is developed to analyze dynamical polarization of itinerant carrier spins and localized magnetic moments under circularly polarized optical excitation and the corresponding band modifications. The results illustrate that nonlinear effects such as optical bistability and self-opacity can indeed be achieved efficiently for a range of excitation power and frequency. In particular, the addition of magnetic dopants is shown to reduce the optical power required for the necessary band shifts by four orders of magnitude compared to that via the optical Stark effect in a nonmagnetic counterpart. Further investigation in a multidimensional parameter space elucidates the conditions for practical realization of the desired nonlinear effects in 2D TMD monolayers.}, number={21}, journal={PHYSICAL REVIEW B}, author={Regan, Malcolm J. and Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Dec} }
 @article{xu_semenov_kim_2020, title={Spin wave generation via localized spin-orbit torque in an antiferromagnet-topological insulator heterostructure}, volume={128}, ISSN={["1089-7550"]}, DOI={10.1063/5.0010478}, abstractNote={The spin–orbit torque induced by a topological insulator (TI) is theoretically examined for spin wave generation in a neighboring antiferromagnetic thin film. The investigation is based on the micromagnetic simulation of Néel vector dynamics and the analysis of transport properties in the TI. The results clearly illustrate that propagating spin waves can be achieved in the antiferromagnetic thin-film strip through localized excitation, traveling over a long distance. The oscillation amplitude gradually decays due to the non-zero damping as the Néel vector precesses around the magnetic easy axis with a fixed frequency. The frequency is also found to be tunable via the strength of the driving electrical current density. While both the bulk and the surface states of the TI contribute to induce the effective torque, the calculation indicates that the surface current plays a dominant role over the bulk counterpart except in the heavily degenerate cases. Compared to the more commonly applied heavy metals, the use of a TI can substantially reduce the threshold current density to overcome the magnetic anisotropy, making it an efficient choice for spin wave generation. The Néel vector dynamics in the nano-oscillator geometry are examined as well.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Jul} }
 @article{semenov_duan_li_kim_2019, title={Conductance nonreciprocity on the surface of a topological insulator with magnetic electrodes}, volume={128}, ISSN={["1879-2553"]}, DOI={10.1016/j.jpcs.2017.07.020}, abstractNote={Asymmetric electrical conductance is theoretically demonstrated on the surface of a topological insulator (TI) in the limit of infinitesimally small forward and reverse biases between two spin selective electrodes. The discontinuous behavior relies on the spin-momentum interlocked nature of TI surface electrons together with the resulting imbalance in the coupling coefficients between the electrodes and TI surface states. The analysis is based on a transmission matrix model that, in combination with a phenomenological treatment for the diffusive limit, accounts for both ballistic and scattered paths simultaneously. With the estimated conductance asymmetry over a factor of 10, implementations in the ratchet-like applications and low-voltage rectification circuits are potentially practicable.}, journal={JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS}, author={Semenov, Yuriy G. and Duan, Xiaopeng and Li, Xi-Lai and Kim, Ki Wook}, year={2019}, month={May}, pages={196–201} }
 @article{semenov_xu_kim_2019, title={Controllable Dispersion of Domain-Wall Movement in Antiferromagnetic Thin Films at Finite Temperatures}, volume={11}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.11.064051}, abstractNote={The dynamics of a 90$^{\circ }$ domain wall in an antiferromagnetic nanostrip driven by the current-induced spin-orbital torque are theoretically examined in the presence of random thermal fluctuations. A soliton-type equation of motion is developed on the basis of energy balance between the driving forces and dissipative processes in terms of the domain wall velocity. Comparison with micromagnetic simulations in the deterministic conditions shows good agreement in both the transient and steady-state transport. When the effects of random thermal fluctuations are included via a stochastic treatment, the results clearly indicate that the dispersion in the domain wall position can be controlled electrically by tailoring the strength and duration of the driving current mediating the spin orbital torque in the antiferromagnet. More specifically, the standard deviation of the probability distribution function for the domain wall movement can be tuned widely while maintaining the average position unaffected. Potential applications of this unusual functionality include the probabilistic computing such as Bayesian learning.}, number={6}, journal={PHYSICAL REVIEW APPLIED}, author={Semenov, Yuriy G. and Xu, Xinyi and Kim, Ki Wook}, year={2019}, month={Jun} }
 @article{xu_li_semenov_kim_2019, title={Creation and Destruction of Skyrmions via Electrical Modulation of Local Magnetic Anisotropy in Magnetic Thin Films}, volume={11}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.11.024051}, abstractNote={Magnetic skyrmions are topologically protected spin textures that are promising as carriers of information for computing and storage beyond CMOS-based systems. An electrostatic approach to creating a skyrmion can be more energy efficient than those based on a driving current. In this work, formation and dissolution of N\'eel skyrmions are examined theoretically via electrical modulation of magnetic anisotropy, in both ferromagnetic and antiferromagnetic structures. Simulations clearly illustrate the feasibility of the mechanism, enabling local control for versatility in applications. Also noteworthy is that the dynamical processes involved are much faster in antiferromagnetic materials.}, number={2}, journal={PHYSICAL REVIEW APPLIED}, author={Xu, Xinyi and Li, Xi-Lai and Semenov, Yuriy G. and Kim, Ki Wook}, year={2019}, month={Feb} }
 @article{xu_semenov_kim_2019, title={Electrical generation and propagation of spin waves in antiferromagnetic thin-film nanostrips}, volume={114}, ISSN={["1077-3118"]}, DOI={10.1063/1.5094767}, abstractNote={Electrical generation of terahertz spin waves is theoretically explored in an antiferromagnetic nanostrip via the current-induced spin–orbit torque. The analysis based on micromagnetic simulations clearly illustrates that the Néel-vector oscillations excited at one end of the magnetic strip can propagate in the form of a traveling wave when the nanostrip axis aligns with the magnetic easy-axis. A sizable threshold is observed in the driving current density or the torque to overcome the unfavorable anisotropy as expected. The generated spin waves are found to travel over a long distance, while the angle of rotation undergoes continuous decay in the presence of nonzero damping. The oscillation frequency is tunable via the strength of the spin–orbit torque, reaching the terahertz regime. Other key characteristics of spin waves such as the phase and the chirality can also be modulated actively. The simulation results further indicate the possibility of wavelike superposition between the excited spin oscillations, illustrating its application as an efficient source of spin-wave signals for information processing.}, number={23}, journal={APPLIED PHYSICS LETTERS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2019}, month={Jun} }
 @article{semenov_xu_kim_2019, title={Thermal fluctuations in antiferromagnetic nanostructures}, volume={489}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2019.165457}, abstractNote={A theoretical model is developed that can accurately analyze the effects of thermal fluctuations in antiferromagnetic (AFM) nano-particles. The approach is based on Fourier series representation of the random effective field with cut-off frequencies of physical origin at low and high limits while satisfying the fluctuation-dissipation theorem at the same time. When coupled with the formalism of a Langevin dynamical equation, it can describe the stochastic Néel vector dynamics with the AFM parameters, circumventing the arbitrariness of the commonly used treatments in the micro-magnetic simulations. Subsequent application of the model to spontaneous Néel vector switching provides a thermal stability analysis of the AFM states. The numerical simulation shows that the AFM states are much less prone to the thermally induced accidental flips than the ferromagnetic counterparts, suggesting a longer retention time for the former.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Semenov, Yuriy G. and Xu, Xiniy and Kim, Ki Wook}, year={2019}, month={Nov} }
 @article{semenov_li_kim_2017, title={Currentless reversal of Néel vector in antiferromagnets}, volume={95}, ISSN={2469-9950 2469-9969}, url={http://dx.doi.org/10.1103/PhysRevB.95.014434}, DOI={10.1103/physrevb.95.014434}, abstractNote={The bias driven perpendicular magnetic anisotropy is a magneto-electric effect that can realize 90$^\circ$ magnetization rotation and even 180$% ^\circ $ flip along the easy axis in the ferromagnets with a minimal energy consumption. This study theoretically demonstrates a similar phenomenon of the Neel vector reversal via a short electrical pulse that can mediate perpendicular magnetic anisotropy in the antiferromagnets. The analysis based on the dynamical equations as well as the micro-magnetic simulations reveals the important role of the inertial behavior in the antiferromagnets that facilitates the Neel vector to overcome the barrier between two free-energy minima of the bistable states along the easy axis. In contrast to the ferromagnets, this Neel vector reversal does not accompany angular moment transfer to the environment, leading to acceleration in the dynamical response by a few orders of magnitude. Further, a small switching energy requirement of a few attojoules illustrates an added advantage of the phenomenon in low-power spintronic applications.}, number={1}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Li, Xi-Lai and Kim, Ki Wook}, year={2017}, month={Jan} }
 @article{semenov_kim_2016, title={Bias-driven spontaneous spin-valley polarization in monolayer transition-metal dichalcogenides}, volume={93}, ISSN={2469-9950 2469-9969}, url={http://dx.doi.org/10.1103/PhysRevB.93.041414}, DOI={10.1103/physrevb.93.041414}, abstractNote={A physical mechanism that may enable electrical control of carrier spin-valley polarization is theoretically examined in a monolayer transition-metal dichalcogenide (TMD) structure. The idea is based on the interplay between the strongly spin-orbit coupled nature of the TMD band structure and the exchange interaction with a proximate magnet that can spontaneously lift the valley degeneracy when the carrier density exceeds a certain threshold. The analysis based on the free energy of the system clearly illustrates the desired spin-valley polarization in the TMD layer as well as the accompanying rotational phase transition in the magnetization. Numerical estimates utilizing the ${\mathrm{WS}}_{2}$ parameters as an example indicate a sharp transition in the spin-valley polarization over tens of percent at room temperature with only a modest change in the electrochemical potential of a few meV via electrostatic bias. Detection of the predicted phenomenon is expected to be straightforward through the corresponding modification in the TMD channel conductance.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2016}, month={Jan} }
 @article{debus_ivanov_ryabchenko_yakovlev_maksimov_semenov_braukmann_rautert_low_godlewski_et al._2016, title={Resonantly enhanced spin-lattice relaxation of Mn2+ ions in diluted magnetic (Zn,Mn)Se/(Zn,Be) Se quantum wells}, volume={93}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.93.195307}, abstractNote={The dynamics of spin-lattice relaxation in the magnetic ${\mathrm{Mn}}^{2+}$ ion system of (Zn,Mn)Se/(Zn,Be)Se quantum-well structures are studied using optical methods. Pronounced cusps are found in the giant Zeeman shift of the quantum-well exciton photoluminescence at specific magnetic fields below 10 T, when the Mn spin system is heated by photogenerated carriers. The spin-lattice relaxation time of the Mn ions is resonantly accelerated at the cusp magnetic fields. Our theoretical analysis demonstrates that a cusp occurs at a spin-level mixing of single ${\mathrm{Mn}}^{2+}$ ions and a quick-relaxing cluster of nearest-neighbor Mn ions, which can be described as intrinsic cross-relaxation resonance within the Mn spin system.}, number={19}, journal={PHYSICAL REVIEW B}, author={Debus, J. and Ivanov, V. Yu. and Ryabchenko, S. M. and Yakovlev, D. R. and Maksimov, A. A. and Semenov, Yu. G. and Braukmann, D. and Rautert, J. and Low, U. and Godlewski, M. and et al.}, year={2016}, month={May} }
 @article{duan_li_li_semenov_kim_2015, title={Highly efficient conductance control in a topological insulator based magnetoelectric transistor}, volume={118}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4937407}, DOI={10.1063/1.4937407}, abstractNote={The spin-momentum interlocked properties of the topological insulator (TI) surface states are exploited in a transistor-like structure for efficient conductance control in the TI-magnet system. Combined with the electrically induced magnetization rotation as part of the gate function, the proposed structure takes advantage of the magnetically modulated TI electronic band dispersion in addition to the conventional electrostatic barrier. The transport analysis coupled with the magnetic simulation predicts super-steep current-voltage characteristics near the threshold along with the GHz operating frequencies. Potential implementation to a complementary logic is also examined. The predicted characteristics are most suitable for applications requiring low power or those with small signals.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Duan, Xiaopeng and Li, Xi-Lai and Li, Xiaodong and Semenov, Yuriy G. and Kim, Ki Wook}, year={2015}, month={Dec}, pages={224502} }
 @article{duan_li_semenov_kim_2015, title={Nonlinear magnetic dynamics in a nanomagnet–topological insulator heterostructure}, volume={92}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.92.115429}, DOI={10.1103/physrevb.92.115429}, abstractNote={Magnetization dynamics of a nanomagnet, when strongly coupled with a topological insulator (TI) via the proximity interaction, is examined theoretically in the presence of electrical current on the TI surface under realistic transport conditions. Due to the spin-momentum interlock, the magnetic state and TI electron transport depend significantly on each other. Such an interdependence leads to a variety of nonlinear dynamical responses in all transport regimes including the scattering dominant diffusive cases. Generation of the anomalous Hall current, in particular, is found to be a key to the unique features that have not been observed previously. For instance, the anomalous Hall current can result in antiparallel alignment of the final magnetization state in reference to the effective driving magnetic field by inducing an extra term that counters the damping effect. Similarly the calculation also reveals steady oscillation of the magnetization under a broad range of conditions, offering a robust mechanism for highly efficient magnetization reversal and/or spin wave excitation under a dc bias.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Duan, Xiaopeng and Li, Xi-Lai and Semenov, Yuriy G. and Kim, Ki Wook}, year={2015}, month={Sep} }
 @article{mai_semenov_barrette_yu_jin_cao_kim_gundogdu_2014, title={Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy}, volume={90}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.90.041414}, DOI={10.1103/physrevb.90.041414}, abstractNote={We measured the lifetime of optically created valley polarization in single layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). However the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single layer WS2. One process involves direct scattering of excitons from K to K' valleys with a spin flip-flop interaction. The other mechanism involves scattering through spin degenerate Gamma valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Gamma and K valleys.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Mai, Cong and Semenov, Yuriy G. and Barrette, Andrew and Yu, Yifei and Jin, Zhenghe and Cao, Linyou and Kim, Ki Wook and Gundogdu, Kenan}, year={2014}, month={Jul} }
 @inproceedings{duan_li_semenov_kim_2014, title={Proposal of a topological insulator based magnetoelectric transistor}, DOI={10.1109/drc.2014.6872341}, abstractNote={A new type of transistor is proposed based on wave-guiding phenomena of topological insulator (TI) surface electrons for applications in CMOS-like circuits and switchable interactions in spin logic circuits. The carrier channel is patterned by the magnetic strip and the ON/OFF switch is achieved by the electrically controlled magnetic valve (Fig. 1A). We characterized the current-gate voltage (Id-Vg) relation and the time resolved performance. Very low subthreshold swing (below 10 mV/dec) and operating frequency above 1 GHz are expected.}, booktitle={2014 72nd annual device research conference (drc)}, author={Duan, X. P. and Li, X. D. and Semenov, Y. G. and Kim, K. W.}, year={2014}, pages={149–150} }
 @article{duan_li_semenov_kim_2014, title={Quasi-optical electron transport across a magnetically induced junction on a topological insulator surface}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4903798}, DOI={10.1063/1.4903798}, abstractNote={Quasi-optical Dirac electron transport is theoretically analyzed at the magnetic boundaries on a topological insulator (TI) surface. The electronic band mismatch induced by the spatially varying magnetization profile can form an effective junction akin to the electrostatic potential step. The transmission/reflection characteristics show a direct dependence on electron energy and incident angle with highly asymmetric patterns. The investigation also illustrates a nontrivial anomalous Hall current along the boundary which is further shown by a numerical simulation based on the finite-difference time-domain method. The results provide key design guidelines for prospective quasi-optical devices based on the TI-magnet heterostructures.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Duan, Xiaopeng and Li, Xiaodong and Semenov, Yuriy G. and Kim, Ki Wook}, year={2014}, month={Dec}, pages={224301} }
 @article{duan_semenov_kim_2014, title={Spin Logic via Controlled Correlation in Nanomagnet–Dirac-Fermion Heterostructures}, volume={2}, ISSN={2331-7019}, url={http://dx.doi.org/10.1103/PhysRevApplied.2.044003}, DOI={10.1103/physrevapplied.2.044003}, abstractNote={A hybrid structure combining the advantages of topological insulator (TI), dielectric ferromagnet (FM), and graphene is investigated to realize the electrically controlled correlation between electronic and magnetic subsystems for low-power, high-functional applications. Two-dimensional Dirac fermion states provide an ideal environment to facilitate strong coupling through the surface interactions with proximate materials. The unique properties of FM-TI and FM-graphene interfaces make it possible for active "manipulation" and "propagation", respectively, of the information state variable based solely on the spin logic platform through electrical gate biases. Our theoretical analysis verifies the feasibility of the concept for logic application with both current-driven and current-less interconnect approaches. The device/circuit characteristics are also examined in realistic conditions, suggesting the desired low-power performance with the estimated energy consumption for COPY/NOT as low as the \textit{attojoule} level.}, number={4}, journal={Physical Review Applied}, publisher={American Physical Society (APS)}, author={Duan, Xiaopeng and Semenov, Yuriy G. and Kim, Ki Wook}, year={2014}, month={Oct} }
 @article{li_semenov_kim_2014, title={Thin-film topological insulator-ferromagnet heterostructures for terahertz detection}, volume={104}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4865423}, DOI={10.1063/1.4865423}, abstractNote={An atomically thin topological insulator is investigated theoretically for long-wavelength photodetection when it interacts with a magnetic material. Through the coupling between top and bottom surfaces as well as the exchange interaction with the proximate ferromagnet, the distribution of optically excited carriers exhibits unique patterns that depend sensitively on the frequency of the incoming light. This effect results in the generation of strong nonzero photocurrent, leading potentially to room-temperature detection of far-infrared/THz radiation with the advantage of low noise and fast response. The ease of frequency tuning by an external electrical bias offers an added versatility in the realistic implementation.}, number={6}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Li, Xiaodong and Semenov, Yuriy G. and Kim, Ki Wook}, year={2014}, month={Feb}, pages={061116} }
 @article{semenov_duan_kim_2014, title={Voltage-driven magnetic bifurcations in nanomagnet–topological insulator heterostructures}, volume={89}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.89.201405}, DOI={10.1103/physrevb.89.201405}, abstractNote={Multiplicity of magnetization dynamics in a thin insulating ferromagnet deposited on a topological insulator (TI) is studied as a function of electron flow at the interface. The spin current of TI surface electrons induces magnetization precession in the magnet, which in turn modifies the TI spin polarization. In contrast to the conventional linear analysis, the self-consistent nature of the interaction leads to auto-oscillation, magnetization reversal, or magnetic deviation under a dc bias, all of which are accompanied by the strong anomalous Hall effect. With a minimal energy requirement as low as tens of aJ, the proposed mechanism offers a highly efficient alternative to the spin transfer torque or spin-Hall based approaches.Received 5 February 2014DOI:https://doi.org/10.1103/PhysRevB.89.201405©2014 American Physical Society}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Duan, Xiaopeng and Kim, Ki Wook}, year={2014}, month={May} }
 @article{mai_barrette_yu_semenov_kim_cao_gundogdu_2013, title={Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2}, volume={14}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl403742j}, DOI={10.1021/nl403742j}, abstractNote={Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization.}, number={1}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Mai, Cong and Barrette, Andrew and Yu, Yifei and Semenov, Yuriy G. and Kim, Ki Wook and Cao, Linyou and Gundogdu, Kenan}, year={2013}, month={Dec}, pages={202–206} }
 @article{semenov_duan_kim_2012, title={Electrically controlled magnetization in ferromagnet-topological insulator heterostructures}, volume={86}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.86.161406}, DOI={10.1103/physrevb.86.161406}, abstractNote={An approach to the electrostatic control of $90^{\circ}$ magnetization rotation in the hybrid structures composed of topological insulators (TIs) and adjacent ferromagnetic insulators (FMI) is proposed and studied. The concept is based on TI electron energy variation with in-plane to put-of plane FMI magnetization turn. The calculations explicitly expose the effect of free energy variability in the form of the electrically controlled uniaxial magnetic anisotropy, which depends on proximate exchange interaction and TI surface electron density. Combining with inherent anisotropy, the magnetization rotation from in-plane to out-of-plane direction is shown to be realizable for 1.7~2.7 ns under the electrical variation of TI chemical potential in the range $\pm$ 100 meV around Dirac point. When bias is withdrawn a small signal current can target the out-of-plane magnetization instable state to the desirable direction of in-plane easy axis, thus the structure can lay the foundation for low energy nonvolatile memory prototype.}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Duan, Xiaopeng and Kim, Ki Wook}, year={2012}, month={Oct} }
 @article{duan_stephanovich_semenov_kim_2012, title={Magnetic domain wall transfer via graphene mediated electrostatic control}, volume={101}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4732794}, DOI={10.1063/1.4732794}, abstractNote={A mechanism that enables electrically controlled magnetic domain wall transfer in a ferromagnetic insulator (FMI) is investigated theoretically by utilizing graphene as a crucial mediating material. The concept is grounded on the variability of the exchange interaction energy between a ferromagnetic insulator and a proximate graphene layer with an inhomogeneous carrier density. A memory device prototype is proposed based on the effect that does not require an active current for its intrinsic function. Our analysis illustrates the highly efficient device operation, with an estimated switching energy of 10−16 J for one binary bit of nonvolatile information.}, number={1}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Duan, X. and Stephanovich, V. A. and Semenov, Y. G. and Kim, K. W.}, year={2012}, month={Jul}, pages={013103} }
 @article{semenov_li_kim_2012, title={Tunable photogalvanic effect on topological insulator surfaces via proximity interactions}, volume={86}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.86.201401}, DOI={10.1103/physrevb.86.201401}, abstractNote={An unusual photo-galvanic effect is predicted on the topological insulator surface when its semi-metallic electronic spectrum is modified by an adjacent ferromagnet. The effect is correlated with light absorption in a wide frequency range (from a few to hundreds of meV) and produces a pronounced response that is not only resonant to the photon energy but also tunable by an external electrical bias. The exceptionally strong peak photocurrent of the order of $\mu$A/cm may be achieved at elevated temperatures with the illumination power of 1 W/cm$^2$ in the THz range on Bi$_2$Se$_3$. These advantages could enable room-temperature detection of far-infrared radiation.}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Li, Xiaodong and Kim, Ki Wook}, year={2012}, month={Nov} }
 @article{borysenko_mullen_li_semenov_zavada_nardelli_kim_2011, title={Electron-phonon interactions in bilayer graphene}, volume={83}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.83.161402}, DOI={10.1103/physrevb.83.161402}, abstractNote={K. M. Borysenko, J. T. Mullen, X. Li, Y. G. Semenov, J. M. Zavada, M. Buongiorno Nardelli, 3 and K. W. Kim Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911 Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 CSMD, Oak Ridge National Laboratory, Oak Ridge, TN 37831 Abstract Using calculations from first principles, we demonstrate that intrinsic carrier-phonon scattering in bilayer graphene is dominated by low energy acoustic (and acoustic-like) phonon modes in a framework that bears more resemblance with bulk graphite than monolayer graphene. The total scattering rate at low/moderate electron energies can be described by a simple two-phonon model in the deformation potential approximation with effective constants Dac ≈ 15 eV and Dop ≈ 2.8 × 108 eV/cm for acoustic and optical phonons, respectively. With much enhanced acoustic phonon scattering, the low field mobility of intrinsic bilayer graphene is estimated to be significantly smaller than that of the monolayer: μ = 8.4× 104 cm2/V·s}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Borysenko, K. M. and Mullen, J. T. and Li, X. and Semenov, Y. G. and Zavada, J. M. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2011}, month={Apr} }
 @article{kong_semenov_krowne_kim_2011, title={Unusual magnetoresistance in a topological insulator with a single ferromagnetic barrier}, volume={98}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3600330}, DOI={10.1063/1.3600330}, abstractNote={Tunneling surface current through a thin ferromagnetic barrier on a three-dimensional topological insulator is shown to possess an extraordinary response to the orientation of barrier magnetization. In contrast to conventional magnetoresistance devices that are sensitive to the relative alignment of two magnetic layers, a drastic change in the transmission current is achieved by a single layer when its magnetization rotates by 90°. Numerical estimations predict a giant magnetoresistance as large as 800% at room temperature with the proximate exchange energy of 40 meV at the barrier interface. When coupled with electrical control of magnetization direction, this phenomenon may be used to enhance the gating function with potentially sharp turn-on/off for low power applications.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kong, B. D. and Semenov, Y. G. and Krowne, C. M. and Kim, K. W.}, year={2011}, month={Jun}, pages={243112} }
 @article{semenov_zavada_kim_2011, title={Weak ferromagnetism of antiferromagnetic domains in graphene with defects}, volume={84}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.84.165435}, DOI={10.1103/physrevb.84.165435}, abstractNote={Magnetic properties of graphene with randomly distributed magnetic defects/vacancies are studied in terms of the Kondo Hamiltonian in the mean field approximation. It has been shown that graphene with defects undergoes a magnetic phase transition from a paramagnetic to a antiferromagnetic (AFM) phase once the temperature reaches the critical point $T_{N}$. The defect straggling is taken into account as an assignable cause of multiple nucleation into AFM domains. Since each domain is characterized by partial compensating magnetization of the defects associated with different sublattices, together they reveal a super-paramagnetic behavior in a magnetic field. Theory qualitatively describe the experimental data provided the temperature dependence of the AFM domain structure.}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2011}, month={Oct} }
 @article{semenov_zavada_kim_2010, title={Electrically controlled magnetic switching based on graphene-magnet composite structures}, volume={107}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3354066}, DOI={10.1063/1.3354066}, abstractNote={A nonvolatile magnetic switch is proposed by utilizing the unique properties of graphene-ferromagnet composite structures. The basic mechanism relies on the role of graphene in mediating and modulating the effective exchange bias between adjacent magnetic layers, which can lead to electrically controlled rotation of magnetic bits. Readout of magnetization states is also achieved electrically through the magnetoresistance effect in the graphene channel. The proposed switch can be used to realize both the memory and programmable logic elements. Theoretical estimates illustrate the feasibility of the concept as well as its potential advantage of low power consumption (∼10−19 J) for the intrinsic switching operation.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2010}, month={Mar}, pages={064507} }
 @article{semenov_zavada_kim_2010, title={Electron spin relaxation in carbon nanotubes}, volume={82}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.82.155449}, DOI={10.1103/physrevb.82.155449}, abstractNote={The long standing problem of inexplicably short spin relaxation in carbon nanotubes (CNTs) is examined. The curvature-mediated spin-orbital interaction is shown to induce fluctuating electron spin precession causing efficient relaxation in a manner analogous to the Dyakonov-Perel mechanism. Our calculation estimates longitudinal (spin-flip) and transversal (decoherence) relaxation times as short as 150 ps and 110 ps at room temperature, respectively, along with a pronounced anisotropic dependence. Interference of electrons originating from different valleys can lead to even faster dephasing. The results can help clarify the measured data, resolving discrepancies in the literature.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2010}, month={Oct} }
 @article{borysenko_mullen_barry_paul_semenov_zavada_nardelli_kim_2010, title={First-principles analysis of electron-phonon interactions in graphene}, volume={81}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.81.121412}, DOI={10.1103/physrevb.81.121412}, abstractNote={The electron-phonon interaction in monolayer graphene is investigated using density-functional perturbation theory. The results indicate that the electron-phonon interaction strength is of comparable magnitude for all four in-plane phonon branches and must be considered simultaneously. Moreover, the calculated scattering rates suggest an acoustic-phonon contribution that is much weaker than previously thought, revealing an important role of optical phonons even at low energies. Accordingly it is predicted, in good agreement with a recent measurement, that the intrinsic mobility of graphene may be more than an order of magnitude larger than the already high values reported in suspended samples.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Borysenko, K. M. and Mullen, J. T. and Barry, E. A. and Paul, S. and Semenov, Y. G. and Zavada, J. M. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2010}, month={Mar} }
 @article{semenov_zavada_kim_2010, title={Graphene spin capacitor for magnetic field sensing}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3462297}, DOI={10.1063/1.3462297}, abstractNote={An analysis of a magnetic field sensor based on a graphene spin capacitor is presented. The proposed device consists of graphene nanoribbons on top of an insulator material connected to a ferromagnetic source/drain. The time evolution of spin polarized electrons injected into the capacitor can be used for an accurate determination at room temperature of external magnetic fields. Assuming a spin relaxation time of 100 ns, magnetic fields on the order of ∼10 mOe may be detected at room temperature. The observational accuracy of this device depends on the density of magnetic defects and spin relaxation time that can be achieved.}, number={1}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2010}, month={Jul}, pages={013106} }
 @article{semenov_zavada_kim_2008, title={Electrical Control of Exchange Bias Mediated by Graphene}, volume={101}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/PhysRevLett.101.147206}, DOI={10.1103/physrevlett.101.147206}, abstractNote={The role of graphene in mediating the exchange interaction is theoretically investigated when placed between two ferromagnetic dielectric materials. The calculation based on a tight-binding model illustrates that the magnetic interactions at the interfaces affect not only the graphene band structure but also the thermodynamic potential of the system, leading to an effective exchange bias between magnetic layers. The analysis indicates a strong dependence of the exchange bias on the properties of the mediating layer, revealing an efficient mechanism of electrical control even at room temperature.}, number={14}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2008}, month={Oct} }
 @article{borysenko_semenov_kim_zavada_2008, title={Electron spin relaxation via flexural phonon modes in semiconducting carbon nanotubes}, volume={77}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.77.205402}, DOI={10.1103/physrevb.77.205402}, abstractNote={This work considers the $g$-tensor anisotropy induced by the flexural thermal vibrations in one-dimensional structures and its role on electron spin relaxation. In particular, the mechanism of spin-lattice relaxation via flexural modes is theoretically studied for localized and delocalized electronic states in semiconducting carbon nanotubes in the presence of a magnetic field. The calculation of a one-phonon spin-flip process predicts distinctive dependencies of the relaxation rate on temperature, magnetic field, and nanotube diameter. A comparison to the spin relaxation caused by the hyperfine interaction clearly suggests the relative efficiency of the proposed mechanism at sufficiently high temperatures. Specifically, the longitudinal spin relaxation time in the semiconducting carbon nanotubes is estimated to be as short as $30\text{ }\ensuremath{\mu}\text{s}$ at room temperature.}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Borysenko, K. M. and Semenov, Y. G. and Kim, K. W. and Zavada, J. M.}, year={2008}, month={May} }
 @article{enaya_semenov_zavada_kim_2008, title={Magnetic polaron for a spin memory application}, volume={104}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3000482}, DOI={10.1063/1.3000482}, abstractNote={A memory concept based on the interfacial exchange energy between itinerant holes in a quantum dot and magnetic ions in an adjacent magnetic insulator is theoretically investigated. A model based on the free energy analysis demonstrates the existence of bistable states through the mechanism of bound collective magnetic polaron, whose formation and dissolution can be controlled electrically via a gate bias pulse. The parameter window suitable for bistability is discussed along with the conditions that support maximum nonvolatility. The analysis is extended to the influence of material choices as well as different designs. The calculation results clearly indicate the possibility of room temperature operation, given the availability of insulating ferromagnetic or antiferromagnetic materials whose Curie temperature is above room temperature.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Enaya, H. and Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2008}, month={Oct}, pages={084306} }
 @article{semenov_zavada_kim_2008, title={Magnetoresistance in bilayer graphene via ferromagnet proximity effects}, volume={77}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.77.235415}, DOI={10.1103/physrevb.77.235415}, abstractNote={A drastic modification of electronic band structure is predicted in bilayer graphene when it is placed between two ferromagnetic insulators. Due to the exchange interaction with the proximate ferromagnet, the electronic energy dispersion in the graphene channel strongly depends on the magnetization orientation of two ferromagnetic layers, $\mathbf{M_{1}}$ and $\mathbf{M_{2}} $. While the parallel configuration $\mathbf{M_{1}}= \mathbf{M_{2}}$ leads to simple spin splitting of both conduction and valence bands, an energy gap is induced as soon as the angle $\theta$ between $\mathbf{M_{1}}$ and $% \mathbf{M_{2}}$ becomes non-zero with the maximum achieved at $\theta=\pi$ (i.e., antiparallel alignment). Consequently, bilayer graphene may exhibit a sizable magnetoresistive effect in the current-in-plane configuration. A rough estimate suggests the resistance changes on the order of tens of percent at room temperature. This effect is expected to become more pronounced as the temperatures decreases.}, number={23}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2008}, month={Jun} }
 @article{enaya_semenov_kim_zavada_2008, title={Nonvolatile Memory via Spin Polaron Formation}, volume={7}, ISSN={1536-125X 1941-0085}, url={http://dx.doi.org/10.1109/TNANO.2008.926332}, DOI={10.1109/TNANO.2008.926332}, abstractNote={A nonvolatile memory is explored theoretically by utilizing the magnetic exchange interaction between localized holes and an adjacent ferromagnetic (FM) material. The active device consists of a buried semiconductor quantum dot (QD) and an FM insulating layer that share an interface. The hole population in the QD is controlled by particle transfer with a reservoir of itinerant holes over a permeable barrier. A theoretical model based on the free energy calculation demonstrates the existence of a bistable state through the mechanism of a collective spin polaron, whose formation and dissolution can be manipulated electrically via a gate bias pulse. The parameter space window suitable for bistability is examined along with the conditions that support maximum nonvolatility. The limitation of QD size scaling is analyzed in terms of the bit retention time.}, number={4}, journal={IEEE Transactions on Nanotechnology}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Enaya, H. and Semenov, Y.G. and Kim, K.W. and Zavada, J.M.}, year={2008}, month={Jul}, pages={480–483} }
 @article{semenov_kim_2007, title={Elastic spin-relaxation processes in semiconductor quantum dots}, volume={75}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.75.195342}, DOI={10.1103/physrevb.75.195342}, abstractNote={Electron spin decoherence caused by elastic spin-phonon processes is investigated comprehensively in a zero-dimensional environment. Specifically, a theoretical treatment is developed for the processes associated with the fluctuations in the phonon potential as well as in the electron procession frequency through the spin-orbit and hyperfine interactions in the semiconductor quantum dots. The analysis identifies the conditions (magnetic field, temperature, etc.) in which the elastic spin-phonon processes can dominate over the inelastic counterparts with the electron spin-flip transitions. Particularly, the calculation results illustrate the potential significance of an elastic decoherence mechanism originating from the intervalley transitions in semiconductor quantum dots with multiple equivalent energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity and phonon decay in spin relaxation is also examined along with that of the local effective field fluctuations caused by the stochastic electronic transitions between the orbital states. Numerical estimations are provided for typical GaAs and Si-based quantum dots.}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2007}, month={May} }
 @article{enaya_semenov_kim_zavada_2007, title={Electrical Manipulation of Nonvolatile Spin Cell Based on Diluted Magnetic Semiconductor Quantum Dots}, volume={54}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/TED.2007.894377}, DOI={10.1109/TED.2007.894377}, abstractNote={In this paper, electrical manipulation of a memory cell based on a semiconductor nanostructure consisting of a diluted magnetic semiconductor (DMS) quantum dot (QD) and a reservoir of itinerant holes separated by an energy barrier is investigated theoretically. The operating principle takes advantage of the paramagnetic-ferromagnetic (PM-FM) phase transition mediated by the itinerant holes in the DMS QD that can lead to electrically controlled write/erase operations. Nonvolatility can be achieved when the structure is properly designed to reach a thermodynamic equilibrium at both the PM and FM configurations (i.e., bistability). Assuming a parabolic confining potential in the QD, the performance characteristics of the proposed nanostructure are analyzed including the scalability and the lifetime. An advantage of this memory concept is the extremely small dissipative energy for write/erase functions due to the open-circuit nature of the process. A readout scheme enabling electrical detection, with the repetition rate up to the 10-100-MHz range, is also explored by utilizing only two contacts. Finally, a potential application of the proposed memory cell is discussed as a rudimentary device for logic AND and OR operations}, number={5}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Enaya, Hani and Semenov, Yuriy G. and Kim, K. W. and Zavada, John M.}, year={2007}, month={May}, pages={1032–1039} }
 @article{semenov_kim_iafrate_2007, title={Electron spin relaxation in semiconducting carbon nanotubes: The role of hyperfine interaction}, volume={75}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.75.045429}, DOI={10.1103/physrevb.75.045429}, abstractNote={A theory of electron spin relaxation in semiconducting carbon nanotubes is developed based on the hyperfine interaction with disordered nuclei spins $I=1∕2$ of $^{13}\mathrm{C}$ isotopes. It is shown that strong radial confinement of electrons enhances the electron-nuclear overlap and subsequently electron spin relaxation (via the hyperfine interaction) in the carbon nanotubes. The analysis also reveals an unusual temperature dependence of longitudinal (spin-flip) and transversal (dephasing) relaxation times: the relaxation becomes weaker with the increasing temperature as a consequence of the particularities in the electron density of states inherent in one-dimensional structures. Numerical estimations indicate relatively high efficiency of this relaxation mechanism compared to the similar processes in bulk diamond. However, the anticipated spin relaxation time of the order of $1\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in carbon nanotubes is still much longer than those found in conventional semiconductor structures. Moreover, it is found that the curvature effect and subsequent rehybridization of $s$ and $p$ orbitals in ultrathin nanotubes may significantly impact the electron spin relaxation leading to its further suppression at certain dimensions.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W. and Iafrate, G. J.}, year={2007}, month={Jan} }
 @article{semenov_kim_zavada_2007, title={Spin field effect transistor with a graphene channel}, volume={91}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2798596}, DOI={10.1063/1.2798596}, abstractNote={A spin field effect transistor (FET) is proposed by utilizing a graphene layer as the channel. Similar to the conventional spin FETs, the device involves spin injection and spin detection by ferromagnetic source and drain. Due to the negligible spin-orbit coupling in the carbon based materials, spin manipulation in the channel is achieved via electrical control of the electron exchange interaction with a ferromagnetic gate dielectric. Numerical estimates indicate the feasibility of the concept if the bias can induce a change in the exchange interaction energy of the order of meV. When nanoribbons are used for a finite channel width, those with armchair-type edges can maintain the device stability against the thermal dispersion.}, number={15}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Y. G. and Kim, K. W. and Zavada, J. M.}, year={2007}, month={Oct}, pages={153105} }
 @article{semenov_enaya_kim_2005, title={Bistability in a magnetic and nonmagnetic double-quantum-well structure mediated by the magnetic phase transition}, volume={86}, ISSN={0003-6951}, url={http://dx.doi.org/10.1063/1.1864237}, DOI={10.1063/1.1864237}, abstractNote={The hole distribution in a double-quantum-well (QW) structure consisting of a magnetic and a nonmagnetic semiconductor QW is investigated as a function of temperature, the energy shift between the QWs, and other relevant parameters. When the itinerant holes mediate the ferromagnetic ordering, it is shown that a bistable state can be formed through hole redistribution, resulting in a significant change in the properties of the constituting magnetic QW (i.e., the paramagnetic-ferromagnetic transition). The model calculation also indicates a large window in the system parameter space where bistability is possible. Hence, this structure could form the basis of a stable memory element that may be scaled down to a few-hole regime.}, number={7}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Y. G. and Enaya, H. and Kim, K. W.}, year={2005}, pages={073107} }
 @article{semenov_kim_2004, title={Correlation of phonon decay with localized electron spin-phase diffusion}, volume={70}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.70.085305}, DOI={10.1103/physrevb.70.085305}, abstractNote={A spin decoherence mechanism is proposed for localized electrons. The irregular phonon phase disturbances originated from phonon relaxation can influence electron spin precession with a net effect of spin phase decay. A quantitative analysis demonstrates relatively high efficiency of this mechanism in the low temperature and low magnetic field regime compared to the spin-flip processes.}, number={8}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2004}, month={Aug} }
 @article{semenov_kim_2004, title={Phonon-Mediated Electron-Spin Phase Diffusion in a Quantum Dot}, volume={92}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/PhysRevLett.92.026601}, DOI={10.1103/physrevlett.92.026601}, abstractNote={An effective spin relaxation mechanism that leads to electron spin decoherence in a quantum dot is proposed. In contrast with the common calculations of spin-flip transitions between the Kramers doublets, we take into account a process of phonon-mediated fluctuation in the electron spin preces-sion and subsequent spin phase diffusion. Specifically, we consider modulations in the longitudinal g factor and hyperfine interaction induced by the phonon-assisted transitions between the lowest electronic states. Prominent differences in the temperature and magnetic field dependence between the proposed mechanism and the spin-flip transitions are expected to facilitate its experimental verification. Numerical estimation demonstrates highly efficient spin relaxation in typical semiconductor quantum dots.}, number={2}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2004}, month={Jan} }
 @article{semenov_kim_2004, title={Spin polaron and bistability in ferromagnetic semiconductor quantum structures}, volume={70}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.70.125303}, DOI={10.1103/physrevb.70.125303}, abstractNote={This work shows that the in-plane localization of a hole confined in a ferromagnetic semiconductor quantum well (QW) can lead to significant energy gain if spontaneous easy-plane magnetization is mediated by the mechanisms other than itinerant carriers. The hole spin normal to the QW plane reorients the in-plane magnetization of the ferromagnetic layer at the location of polaron formation, resulting in an exchange potential with a discrete level of localization. A flexible model that incorporates the magnetization gradient term, as well as magnetic anisotropy, is proposed. In contrast to the calculations of magnetic polaron in the paramagnetic semiconductors, the energy of spin polaron in a ferromagnetic semiconductor is almost independent of the temperature in a wide range below the critical temperature of phase transition. Our calculation also demonstrates the existence of bistability in the hole state when the structure consists of appropriate ferromagnetic and nonmagnetic QWs separated by a finite barrier. Hence, a memory element that can be scaled down to a single hole may be achieved through polaron formation.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2004}, month={Sep} }