@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{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{li_duan_kim_2014, title={Controlling electron propagation on a topological insulator surface via proximity interactions}, volume={89}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.89.045425}, DOI={10.1103/physrevb.89.045425}, abstractNote={The possibility of electron beam guiding is theoretically explored on the surface of a topological insulator through the proximity interaction with a magnetic material. The electronic band modification induced by the exchange coupling at the interface defines the path of electron propagation in analogy to the optical fiber for photons. Numerical simulations indicate the guiding efficiency is much higher than that in the ``waveguide'' formed by an electrostatic potential barrier such as $p$-$n$ junctions. Furthermore, the results illustrate effective flux control and beam steering that can be realized by altering the magnetization/spin texture of the adjacent magnetic materials. Specifically, the feasibility to switch on and off and make a large-angle turn is demonstrated under realistic conditions. Potential implementation to logic and interconnect applications is also examined in connection with electrically controlled magnetization switching.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Li, Xiaodong and Duan, Xiaopeng and Kim, Ki Wook}, year={2014}, month={Jan} }
 @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{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{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} }