@article{arnault_al-tawhid_salmani-rezaie_muller_kumah_bahramy_finkelstein_ahadi_2023, title={Anisotropic superconductivity at KTaO3(111) interfaces}, volume={9}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.adf1414}, DOI={10.1126/sciadv.adf1414}, abstractNote={
            A two-dimensional, anisotropic superconductivity was recently found at the KTaO
            3
            (111) interfaces. The nature of the anisotropic superconducting transition remains a subject of debate. To investigate the origins of the observed behavior, we grew epitaxial KTaO
            3
            (111)-based heterostructures. We show that the superconductivity is robust against the in-plane magnetic field and violates the Pauli limit. We also show that the Cooper pairs are more resilient when the bias is along [11
            
              
                
                  2
                  ¯
                
              
            
            ] (I ∥ [11
            
              
                
                  2
                  ¯
                
              
            
            ]) and the magnetic field is along [1
            
              
                
                  1
                  ¯
                
              
            
            0] (
            B
            ∥ [1
            
              
                
                  1
                  ¯
                
              
            
            0]). We discuss the anisotropic nature of superconductivity in the context of electronic structure, orbital character, and spin texture at the KTaO
            3
            (111) interfaces. The results point to future opportunities to enhance superconducting transition temperatures and critical fields in crystalline, two-dimensional superconductors with strong spin-orbit coupling.
          }, number={7}, journal={SCIENCE ADVANCES}, author={Arnault, Ethan G. and Al-Tawhid, Athby H. and Salmani-Rezaie, Salva and Muller, David A. and Kumah, Divine P. and Bahramy, Mohammad S. and Finkelstein, Gleb and Ahadi, Kaveh}, year={2023}, month={Feb} }
 @article{al-tawhid_poage_salmani-rezaie_gonzalez_chikara_muller_kumah_gastiasoro_lorenzana_ahadi_2023, title={Enhanced Critical Field of Superconductivity at an Oxide Interface}, volume={7}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.3c01571}, abstractNote={The nature of superconductivity and its interplay with strong spin-orbit coupling at the KTaO3(111) interfaces remain a subject of debate. To address this problem, we grew epitaxial LaMnO3/KTaO3(111) heterostructures. We show that superconductivity is robust against the in-plane magnetic field, with the critical field of superconductivity reaching ∼25 T in optimally doped heterostructures. The superconducting order parameter is highly sensitive to the carrier density. We argue that spin-orbit coupling drives the formation of anomalous quasiparticles with vanishing magnetic moment, providing significant condensate immunity against magnetic fields beyond the Pauli paramagnetic limit. These results offer design opportunities for superconductors with extreme resilience against the applied magnetic fields.}, journal={NANO LETTERS}, author={Al-Tawhid, Athby H. H. and Poage, Samuel J. J. and Salmani-Rezaie, Salva and Gonzalez, Antonio and Chikara, Shalinee and Muller, David A. A. and Kumah, DivineP. P. and Gastiasoro, Maria N. N. and Lorenzana, Josei and Ahadi, Kaveh}, year={2023}, month={Jul} }
 @article{schwaigert_salmani-rezaie_barone_paik_ray_williams_muller_schlom_ahadi_2023, title={Molecular beam epitaxy of KTaO3}, volume={41}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0002223}, DOI={10.1116/6.0002223}, abstractNote={Strain-engineering is a powerful means to tune the polar, structural, and electronic instabilities of incipient ferroelectrics. KTaO3 is near a polar instability and shows anisotropic superconductivity in electron-doped samples. Here, we demonstrate growth of high-quality KTaO3 thin films by molecular-beam epitaxy. Tantalum was provided by either a suboxide source emanating a TaO2 flux from Ta2O5 contained in a conventional effusion cell or an electron-beam-heated tantalum source. Excess potassium and a combination of ozone and oxygen (10% O3 + 90% O2) were simultaneously supplied with the TaO2 (or tantalum) molecular beams to grow the KTaO3 films. Laue fringes suggest that the films are smooth with an abrupt film/substrate interface. Cross-sectional scanning transmission electron microscopy does not show any extended defects and confirms that the films have an atomically abrupt interface with the substrate. Atomic force microscopy reveals atomic steps at the surface of the grown films. Reciprocal space mapping demonstrates that the films, when sufficiently thin, are coherently strained to the SrTiO3 (001) and GdScO3 (110) substrates.}, number={2}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Schwaigert, Tobias and Salmani-Rezaie, Salva and Barone, Matthew R. and Paik, Hanjong and Ray, Ethan and Williams, Michael D. and Muller, David A. and Schlom, Darrell G. and Ahadi, Kaveh}, year={2023}, month={Mar} }
 @article{ahadi_cadien_2022, title={Complex High-kappa Oxides for Gate Dielectric Applications}, volume={6}, ISSN={["1543-186X"]}, url={https://doi.org/10.1007/s11664-022-09724-2}, DOI={10.1007/s11664-022-09724-2}, journal={JOURNAL OF ELECTRONIC MATERIALS}, publisher={Springer Science and Business Media LLC}, author={Ahadi, Kaveh and Cadien, Ken}, year={2022}, month={Jun} }
 @article{al-tawhid_kanter_hatefipour_irving_kumah_shabani_ahadi_2022, title={Oxygen Vacancy-Induced Anomalous Hall Effect in a Nominally Non-magnetic Oxide}, volume={9}, ISSN={["1543-186X"]}, url={https://doi.org/10.1007/s11664-022-09941-9}, DOI={10.1007/s11664-022-09941-9}, abstractNote={The anomalous Hall effect, a hallmark of broken time-reversal symmetry and spin-orbit coupling, is frequently observed in magnetically polarized systems. Its realization in non-magnetic systems, however, remains elusive. Here, we report on the observation of anomalous Hall effect in nominally non-magnetic KTaO3. Anomalous Hall effect emerges in reduced KTaO3 and shows an extrinsic to intrinsic crossover. A paramagnetic behavior is observed in reduced samples using first principles calculations and quantitative magnetometry. The observed anomalous Hall effect follows the oxygen vacancy-induced magnetization response, suggesting that the localized magnetic moments of the oxygen vacancies scatter conduction electrons asymmetrically and give rise to anomalous Hall effect. The anomalous Hall conductivity becomes insensitive to scattering rate in the low temperature limit (T<5 K), implying that the Berry curvature of the electrons on the Fermi surface controls the anomalous Hall effect. Our observations describe a detailed picture of many-body interactions, triggering anomalous Hall effect in a non-magnetic system.}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Al-Tawhid, Athby H. and Kanter, Jesse and Hatefipour, Mehdi and Irving, Douglas L. and Kumah, Divine P. and Shabani, Javad and Ahadi, Kaveh}, year={2022}, month={Sep} }
 @article{al-tawhid_kanter_hatefipour_kumah_shabani_ahadi_2022, title={Superconductivity and Weak Anti-localization at KTaO3 (111) Interfaces}, volume={8}, ISSN={["1543-186X"]}, url={https://doi.org/10.1007/s11664-022-09844-9}, DOI={10.1007/s11664-022-09844-9}, abstractNote={The intersection of two-dimensional superconductivity and topologically nontrivial states hosts a wide range of quantum phenomena, including Majorana fermions. Coexistence of topologically nontrivial states and superconductivity in a single material, however, remains elusive. Here, we report on the observation of two-dimensional superconductivity and weak anti-localization at the TiOx/KTaO3(111) interfaces. A remnant, saturating resistance persists below the transition temperature as superconducting puddles fail to reach phase coherence. Signatures of weak anti-localization are observed below the superconducting transition, suggesting the coexistence of superconductivity and weak anti-localization. The superconducting interfaces show roughly one order of magnitude larger weak anti-localization correction, compared to non-superconducting interfaces, alluding to a relatively large coherence length in these interfaces.}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Al-Tawhid, Athby H. and Kanter, Jesse and Hatefipour, Mehdi and Kumah, Divine P. and Shabani, Javad and Ahadi, Kaveh}, year={2022}, month={Aug} }
 @article{ahadi_cadien_2021, title={Hf1-xZrxO2 and HfO2/ZrO2 gate dielectrics with extremely low density of interfacial defects using low temperature atomic layer deposition on GaN and InP}, volume={39}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0000914}, DOI={10.1116/6.0000914}, abstractNote={Achieving a negative capacitance field effect transistor with a subthreshold swing beyond the Boltzmann limit requires a “defect-free” dielectric-semiconductor interface. We grew alloyed (Hf1−xZrxO2) and stacked (HfO2/ZrO2) gate dielectrics on GaN and InP substrates using low temperature plasma enhanced atomic layer deposition. In situ ellipsometry data show that alloying hafnia with zirconia reduces the refractive index and widens the bandgap. The stacked and alloyed structures reveal very low capacitance-voltage hysteresis of 35 and 45 mV, respectively, on GaN. The density of interfacial traps as low as 1.12 × 1010 cm−2 eV−1 was achieved on GaN mainly due to the combination of very low dielectric growth temperature (100 °C) and high postfabrication heat treatment temperature (510 °C). The conduction and valence band offsets of the alloyed gate dielectrics on InP were measured and compared to pure zirconia using a combination of x-ray photoelectron spectroscopy and ellipsometry. The alloyed structures show a wider bandgap, larger conduction band offset, and smaller valence band offset compared to pure zirconia. This was attributed to the increase in the valence band width with hafnia addition, which reduces the alloyed gate dielectric’s valence band offset. We resolved the band structure alignement to be type I with band offsets of 3.53 eV for electrons and 1.03 eV for holes in Hf0.25Zr0.75O2/InP heterojunctions. The results allow for a clear and detailed picture of two distinct growth procedure that affect the interfacial defect concentration.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Ahadi, Kaveh and Cadien, Ken}, year={2021}, month={May} }
 @article{topological quantum matter to topological phase conversion: fundamentals, materials, physical systems for phase conversions, and device applications_2021, year={2021}, month={Feb} }
 @misc{polash_yalameha_zhou_ahadi_nourbakhsh_vashaee_2021, title={Topological quantum matter to topological phase conversion: Fundamentals, materials, physical systems for phase conversions, and device applications}, volume={145}, ISSN={["1879-212X"]}, url={https://doi.org/10.1016/j.mser.2021.100620}, DOI={10.1016/j.mser.2021.100620}, abstractNote={The spin-orbit coupling field, an atomic magnetic field inside a Kramers’ system, or discrete symmetries can create a topological torus in the Brillouin Zone and provide protected edge or surface states, which can contain relativistic fermions, namely, Dirac and Weyl Fermions. The topology-protected helical edge or surface states and the bulk electronic energy band define different quantum or topological phases of matters, offering an excellent prospect for some unique device applications. Device applications of the quantum materials rely primarily on understanding the topological properties, their mutual conversion processes under different external stimuli, and the physical system for achieving the phase conversion. There have been tremendous efforts in finding new topological materials with exotic topological phases. However, the application of the topological properties in devices is still limited due to the slow progress in developing the physical structures for controlling the topological phase conversions. Such control systems often require extreme tuning conditions or the fabrication of complex multi-layered topological structures. This review article highlights the details of the topological phases, their conversion processes, along with their potential physical systems, and the prospective application fields. A general overview of the critical factors for topological phases and the materials properties are further discussed to provide the necessary background for the following sections.}, journal={MATERIALS SCIENCE & ENGINEERING R-REPORTS}, publisher={Elsevier BV}, author={Polash, Md Mobarak Hossain and Yalameha, Shahram and Zhou, Haihan and Ahadi, Kaveh and Nourbakhsh, Zahra and Vashaee, Daryoosh}, year={2021}, month={Jul} }
 @article{al-tawhid_kumah_ahadi_2021, title={Two-dimensional electron systems and interfacial coupling in LaCrO3/KTaO3 heterostructures}, volume={118}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0049119}, DOI={10.1063/5.0049119}, abstractNote={The strong interfacial coupling at the 3d-5d transition metal-oxide interfaces has generated excitement due to the possibility of engineering a wide range of quantum phenomena and functionalities. Here, we investigate the electronic interfacial coupling and structural properties of LaCrO3/KTaO3 heterostructures. High-quality LaCrO3 films were grown on KTaO3 substrates using molecular beam epitaxy. These heterostructures show a robust two-dimensional electron gas and a metallic behavior down to liquid helium temperature. Using magnetoresistance measurements, we analyze the coupling of electronic orders between Cr 3d and Ta 5d states and observe signatures of weak anti-localization and Kondo scattering at low-temperature transport. The results provide direct evidence that a crossover (weak anti-localization to Kondo) occurs with increasing temperature as the dephasing scattering events reduce the coherence length. Our observations allow for a clear and detailed picture of two distinct quantum corrections to conductivity at low temperature.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Al-Tawhid, Athby H. and Kumah, Divine P. and Ahadi, Kaveh}, year={2021}, month={May} }
 @article{al-tawhid_shafe_bagheri_guan_reddy_mita_moody_collazo_sitar_ahadi_2021, title={Weak localization and dimensional crossover in compositionally graded AlxGa1-xN}, volume={118}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0042098}, DOI={10.1063/5.0042098}, abstractNote={The interaction between the itinerant carriers, lattice dynamics, and defects is a problem of long-standing fundamental interest for developing quantum theory of transport. Here, we study this interaction in the compositionally and strain-graded AlGaN heterostructures grown on AlN substrates. The results provide direct evidence that a dimensional crossover (2D–3D) occurs with increasing temperature as the dephasing scattering events reduce the coherence length. These heterostructures show a robust polarization-induced 3D electron gas and a metallic-like behavior down to liquid helium temperature. Using magnetoresistance measurements, we analyze the evolution of the interaction between charge carriers, lattice dynamics, and defects as a function of temperature. A negative longitudinal magnetoresistance emerges at low temperatures, in line with the theory of weak localization. A weak localization fit to near zero-field magneto-conductance indicates a coherence length that is larger than the elastic mean free path and film thickness (lφ>t>lel), suggesting a 2D weak localization in a three-dimensional electron gas. Our observations allow for a clear and detailed picture of two distinct localization mechanisms that affect carrier transport at low temperature.}, number={8}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Al-Tawhid, Athby and Shafe, Abdullah-Al and Bagheri, Pegah and Guan, Yan and Reddy, Pramod and Mita, Seiji and Moody, Baxter and Collazo, Ramon and Sitar, Zlatko and Ahadi, Kaveh}, year={2021}, month={Feb} }
 @article{correlating magnetic structure and magnetotransport in semimetal thin films of 
eu1−xsmxtio3_2020, url={http://dx.doi.org/10.1103/physrevmaterials.4.054411}, DOI={10.1103/physrevmaterials.4.054411}, abstractNote={We report on the evolution of the average and depth-dependent magnetic order in thin-film samples of biaxially stressed and electron-doped EuTiO3 for samples across a doping range < 0.1 to 7.8 × 1020 cm-3. Under an applied in-plane magnetic field, the G-type antiferromagnetic ground state undergoes a continuous spin-flop phase transition into in-plane, field-polarized ferromagnetism. The critical field for ferromagnetism slightly decreases with an increasing number of free carriers, yet the field evolution of the spin-flop transition is qualitatively similar across the doping range. Unexpectedly, we observe interfacial ferromagnetism with saturated Eu2+ moments at the substrate interface at low fields preceding ferromagnetic saturation throughout the bulk of the degenerate semiconductor film. We discuss the implications of these findings for the unusual magnetotransport properties of this compound.}, journal={Physical Review Materials}, year={2020}, month={May} }
 @article{high current density smtio3/srtio3 field-effect transistors_2020, url={http://dx.doi.org/10.1021/acsaelm.9b00738}, DOI={10.1021/acsaelm.9b00738}, abstractNote={SmTiO3/SrTiO3 interfaces are of potential interest for electronic devices as they exhibit novel electronic phenomena such as metal–insulator transitions. However, good transistor performance from t...}, journal={ACS Applied Electronic Materials}, year={2020}, month={Feb} }
 @article{magnetoelastic coupling to coherent acoustic phonon modes in the ferrimagnetic insulator 
gdtio3_2020, url={http://dx.doi.org/10.1103/physrevb.102.085138}, DOI={10.1103/physrevb.102.085138}, abstractNote={In this work we investigate single crystal $\mathrm{Gd}\mathrm{Ti}{\mathrm{O}}_{3}$, a promising candidate material for Floquet engineering and magnetic control, using ultrafast optical pump-probe reflectivity and magneto-optical Kerr spectroscopy. $\mathrm{Gd}\mathrm{Ti}{\mathrm{O}}_{3}$ is a Mott-Hubbard insulator with a ferrimagnetic and orbitally ordered ground state (${T}_{C}$ = 32 K). We observe multiple signatures of the magnetic phase transition in the photoinduced reflectivity signal, in response to above band-gap 660-nm excitation. Magnetic dynamics measured via Kerr spectroscopy reveal optical perturbation of the ferrimagnetic order on spin-lattice coupling timescales, highlighting the competition between the ${\mathrm{Gd}}^{3+}$ and ${\mathrm{Ti}}^{3+}$ magnetic sub-lattices. Furthermore, a strong coherent oscillation is present in the reflection and Kerr dynamics, attributable to an acoustic strain wave launched by the pump pulse. The amplitude of this acoustic mode is highly dependent on the magnetic order of the system, growing sharply in magnitude at ${T}_{C}$, indicative of strong magneto-elastic coupling. The driving mechanism, involving strain-induced modification of the magnetic exchange interaction, implies an indirect method of coupling light to the magnetic degrees of freedom and emphasizes the potential of $\mathrm{Gd}\mathrm{Ti}{\mathrm{O}}_{3}$ as a tunable quantum material.}, journal={Physical Review B}, year={2020}, month={Aug} }
 @article{order-disorder ferroelectric transition of strained 
srtio3_2020, url={http://dx.doi.org/10.1103/physrevlett.125.087601}, DOI={10.1103/physrevlett.125.087601}, abstractNote={SrTiO_{3} is an incipient ferroelectric that is believed to exhibit a prototype displacive, soft mode ferroelectric transition when subjected to mechanical stress or alloying. We use high-angle annular dark-field imaging in scanning transmission electron microscopy to reveal local polar regions in the room-temperature, paraelectric phase of strained SrTiO_{3} films, which undergo a ferroelectric transition at low temperatures. These films contain nanometer-sized domains in which the Ti columns are displaced. In contrast, these nanodomains are absent in unstrained films, which do not become ferroelectric. The results show that the ferroelectric transition of strained SrTiO_{3} is an order-disorder transition. We discuss the impact of the results on the nature of the ferroelectric transition of SrTiO_{3}.}, journal={Physical Review Letters}, year={2020}, month={Aug} }
 @article{polar nanodomains in a ferroelectric superconductor_2020, url={http://dx.doi.org/10.1021/acs.nanolett.0c02285}, DOI={10.1021/acs.nanolett.0c02285}, abstractNote={TThe mechanisms by which itinerant carriers compete with polar crystal distortions is a key unresolved issue for polar superconductors, which offer new routes to unconventional Cooper pairing. Strained, doped SrTiO3 films undergo successive ferroelectric and superconducting transitions, making them ideal candidates to elucidate the nature of this competition. Here, we reveal these interactions using scanning transmission electron microscopy studies of the evolution of polar nanodomains as a function of doping. These nanodomains are a precursor to the ferroelectric phase and a measure of long-range Coulomb interactions. With increasing doping, the magnitude of the polar displacements, the nanodomain size, and the Curie temperature are systematically suppressed. In addition, we show that disorder caused by the dopant atoms themselves presents a second contribution to the destabilization of the ferroelectric state. The results provide evidence for two distinct mechanisms that suppress the polar transition with doping in a ferroelectric superconductor.}, journal={Nano Letters}, year={2020}, month={Aug} }
 @article{possible signatures of mixed-parity superconductivity in doped polar 
srtio3
 films_2020, url={http://dx.doi.org/10.1103/physrevb.101.100503}, DOI={10.1103/physrevb.101.100503}, abstractNote={Superconductors that possess both broken spatial inversion symmetry and spin-orbit interactions exhibit a mix of spin singlet and triplet pairing. Here, we report on measurements of the superconducting properties of electron-doped, strained $\mathrm{SrTi}{\mathrm{O}}_{3}$ films. These films have an enhanced superconducting transition temperature and were previously shown to undergo a transition to a polar phase prior to becoming superconducting. We show that some films show signatures of an unusual superconducting state, such as an in-plane critical field that is higher than both the paramagnetic and orbital pair breaking limits. Moreover, nonreciprocal transport, which reflects the ratio of odd versus even pairing interactions, is observed. Together, these characteristics indicate that these films provide a tunable platform for investigations of unconventional superconductivity.}, journal={Physical Review B}, year={2020}, month={Mar} }
 @article{probing the polar instability of strained srtio3 with haadf-stem_2020, url={http://dx.doi.org/10.1017/s1431927620021716}, DOI={10.1017/s1431927620021716}, abstractNote={ferroelectricity where ferroelectricity of SrTiO3 can potentially be used to tune the nature of its superconducting state. SrTiO3 is believed to exhibit a prototype displacive, soft mode ferroelectric transition. A hallmark of order-disorder transitions, on the other hand, is the formation of polar domains above the Curie temperature. These polar regions percolate below the Curie temperature to form a longrange ordered ferroelectric state. Images of polar regions above the Curie temperature of ferroelectric}, journal={Microscopy and Microanalysis}, year={2020}, month={Jul} }
 @article{anisotropic magnetoresistance in the itinerant antiferromagnetic 
eutio3_2019, url={http://dx.doi.org/10.1103/physrevb.99.041106}, DOI={10.1103/physrevb.99.041106}, abstractNote={We report on measurements of the anisotropic magnetoresistance (AMR) of doped $\mathrm{EuTi}{\mathrm{O}}_{3}$. It is shown that the primary contribution to the AMR is the crystalline component, which depends on the relative orientation between the magnetic moments and the crystal axes. With increasing magnetic field, a fourfold crystalline AMR undergoes a change in its alignment with respect to the crystal axes. The results are discussed in the context of the coupling between spin canting, electronic structure, and transport. We discuss the potential role of Weyl points in the band structure. At high fields, the AMR transitions to uniaxial symmetry, which is lower than that of the lattice, along with a crossover from positive to negative magnetoresistance.}, journal={Physical Review B}, year={2019}, month={Jan} }
 @article{controlling a van hove singularity and fermi surface topology at a complex oxide heterostructure interface_2019, url={http://dx.doi.org/10.1038/s41467-019-13046-z}, DOI={10.1038/s41467-019-13046-z}, abstractNote={Abstract}, journal={Nature Communications}, year={2019}, month={Dec} }
 @article{enhancing superconductivity in srtio3 films with strain_2019, url={http://dx.doi.org/10.1126/sciadv.aaw0120}, DOI={10.1126/sciadv.aaw0120}, abstractNote={
            A doubling of the superconducting transition temperature occurs in strained SrTiO
            3
            films, which are known to become ferroelectric.
          }, journal={Science Advances}, year={2019}, month={Apr} }
 @article{ferroelectric enhancement of superconductivity in compressively strained 
srtio3
 films_2019, url={http://dx.doi.org/10.1103/physrevmaterials.3.091401}, DOI={10.1103/physrevmaterials.3.091401}, abstractNote={SrTiO$_3$ is an incipient ferroelectric on the verge of a polar instability, which is avoided at low temperatures by quantum fluctuations. Within this unusual quantum paraelectric phase, superconductivity persists despite extremely dilute carrier densities. Ferroelectric fluctuations have been suspected to play a role in the origin of superconductivity by contributing to electron pairing. To investigate this possibility, we used optical second harmonic generation to measure the doping and temperature dependence of the ferroelectric order parameter in compressively strained SrTiO$_3$ thin films. At low temperatures, we uncover a spontaneous out-of-plane ferroelectric polarization with an onset that correlates perfectly with normal-state electrical resistivity anomalies. These anomalies have previously been associated with an enhancement of the superconducting critical temperature in doped SrTiO$_3$ films, directly linking the ferroelectric and superconducting phases. We develop a long-range mean-field Ising model of the ferroelectric phase transition to interpret the data and extract the relevant energy scales in the system. Our results support a long-suspected connection between ferroelectricity and superconductivity in SrTiO$_3$, but call into question the role played by ferroelectric fluctuations.}, journal={Physical Review Materials}, year={2019}, month={Sep} }
 @article{lattice relaxations around individual dopant atoms in 
srtio3_2019, url={http://dx.doi.org/10.1103/physrevmaterials.3.114404}, DOI={10.1103/physrevmaterials.3.114404}, abstractNote={The local atomic structure around individual dopant atoms can directly influence the electronic properties of a doped material. Here, we use quantitative scanning transmission electron microscopy to study the local lattice relaxations around Sm dopant atoms in $\mathrm{SrTi}{\mathrm{O}}_{3}$ thin films. These films have recently been shown to undergo successive ferroelectric and superconducting transitions when strained. We show that neighboring Ti-O columns move away from the columns that contain Sm dopants. The observed displacements are, however, more complex than a simple outward expansion of all four surrounding Ti-O columns. We discuss potential implications, especially for the ferroelectric transition observed in strained films.}, journal={Physical Review Materials}, year={2019}, month={Nov} }
 @article{probing the local lattice distortions in doped srtio3 using quantitative stem_2019, url={http://dx.doi.org/10.1017/s1431927619005610}, DOI={10.1017/s1431927619005610}, abstractNote={SrTiO3 is a cubic perovskite material that has been widely investigated because of its high electron mobility, superconductivity, and high permittivity. Undoped SrTiO3 is a conventional band insulator. It can be doped by substitution of trivalent rare-earth elements (R), such as La or Sm, on the Sr2+ site. Each R ion donates one electron to the conduction band of SrTiO3. In general, local lattice distortions around individual dopant atoms are believed to influence transport properties and their role as dopant atoms. For example, among the possible rare earth dopants, differences exist in ionic radius and other properties, such as number of unpaired f-electrons. Therefore, revealing the effect of individual dopants on the lattice could impact the understanding of the unique transport properties of SrTiO3.}, journal={Microscopy and Microanalysis}, year={2019}, month={Aug} }
 @article{carrier density control of magnetism and berry phases in doped eutio3_2018, url={http://dx.doi.org/10.1063/1.5025317}, DOI={10.1063/1.5025317}, abstractNote={In materials with broken time-reversal symmetry, the Berry curvature acts as a reciprocal space magnetic field on the conduction electrons and is a significant contribution to the magnetotransport properties, including the intrinsic anomalous Hall effect. Here, we report neutron diffraction, transport, and magnetization measurements of thin films of doped EuTiO3, an itinerant magnetic material, as a function of carrier density and magnetic field. These films are itinerant antiferromagnets at all doping concentrations. At low carrier densities, the magnetoresistance indicates a metamagnetic transition, which is absent at high carrier densities (>6 × 1020 cm−3). Strikingly, the crossover coincides with a sign change in the spontaneous Hall effects, indicating a sign change in the Berry curvature. We discuss the results in the context of the band structure topology and its coupling to the magnetic texture.}, journal={APL Materials}, year={2018}, month={May} }
 @article{electron nematic fluid in a strained 
sr3ru2o7
 film_2018, url={http://dx.doi.org/10.1103/physrevb.97.155160}, DOI={10.1103/physrevb.97.155160}, abstractNote={Sr3Ru2O7 belongs to the family of layered strontium ruthenates and exhibits a range of unusual emergent properties, such as electron nematic behavior and metamagnetism. Here, we show that epitaxial film strain significantly modifies these phenomena. In particular, we observe enhanced magnetic interactions and an electron nematic phase that extends to much higher temperatures and over a larger magnetic field range than in bulk single crystals. Furthermore, the films show an unusual anisotropic non-Fermi liquid behavior that is controlled by the direction of the applied magnetic field. At high magnetic fields the metamagnetic transition to a ferromagnetic phase recovers isotropic Fermi-liquid behavior. The results support the interpretation that these phenomena are linked to the special features of the Fermi surface, which can be tuned by both film strain and an applied magnetic field.}, journal={Physical Review B}, year={2018}, month={Apr} }
 @article{spontaneous hall effects in the electron system at the smtio3/eutio3 interface_2018, url={http://dx.doi.org/10.1063/1.5025169}, DOI={10.1063/1.5025169}, abstractNote={Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ∼3.9 × 1014 cm−2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure, and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared to uniformly doped EuTiO3. In particular, the topological Hall effect contribution appears at higher temperatures and the anomalous Hall effect shows a sign change with temperature. The results suggest that interfaces can be used to tune topological phenomena in itinerant magnetic systems.}, journal={APL Materials}, year={2018}, month={May} }
 @article{electric field effect near the metal-insulator transition of a           two-dimensional electron system in srtio3_2017, url={http://dx.doi.org/10.1063/1.4975806}, DOI={10.1063/1.4975806}, abstractNote={SmTiO3/SrTiO3 interfaces exhibit a two-dimensional electron system with carrier densities in the order of 3 × 1014 cm−2 due to the polar discontinuity at the interface. Here, electric field effect is used to investigate an electron system at this interface whose carrier density has been depleted substantially by the gate metal and by reducing the thickness of the SmTiO3. At zero applied gate voltage, the sheet resistance exceeds the quantum resistance, h/e2, by more than an order of magnitude, and the SrTiO3 channel is in the hopping transport regime. The electric field modulates the carrier density in the channel, which approaches the transition to a metal at positive gate bias. The channel resistances are found to scale by a single parameter that depends on the gate voltage, similar to two-dimensional electron systems in high-quality semiconductors.}, journal={Applied Physics Letters}, year={2017}, month={Feb} }
 @article{evidence of a topological hall effect in eu1−xsmxtio3_2017, url={http://dx.doi.org/10.1063/1.4997498}, DOI={10.1063/1.4997498}, abstractNote={We report on the observation of a possible topological Hall effect in thin films of the itinerant ferromagnet Eu1−xSmxTiO3. EuTiO3 and Eu0.955Sm0.045TiO3 films were grown by molecular beam epitaxy. The EuTiO3 film is insulating. The Hall resistivity of the Eu0.955Sm0.045TiO3 films exhibits the anomalous Hall effect below the Curie temperature of ∼5 K and additional features that appear at 2 K. It is shown that these features are magnetic in origin and consistent with the topological Hall effect seen in material systems with topologically nontrivial spin textures such as skyrmions. The results open up interesting possibilities for epitaxial hybrid heterostructures that combine topological magnetic states, tunable carrier densities, and other phenomena.}, journal={Applied Physics Letters}, year={2017}, month={Oct} }
 @article{freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors_2017, url={http://dx.doi.org/10.1007/s12274-017-1573-8}, DOI={10.1007/s12274-017-1573-8}, journal={Nano Research}, year={2017}, month={May} }
 @article{growth of strontium ruthenate films by hybrid molecular beam epitaxy_2017, url={http://dx.doi.org/10.1063/1.4998772}, DOI={10.1063/1.4998772}, abstractNote={We report on the growth of epitaxial Sr2RuO4 films using a hybrid molecular beam epitaxy approach in which a volatile precursor containing RuO4 is used to supply ruthenium and oxygen. The use of the precursor overcomes a number of issues encountered in traditional molecular beam epitaxy that uses elemental metal sources. Phase-pure, epitaxial thin films of Sr2RuO4 are obtained. At high substrate temperatures, growth proceeds in a layer-by-layer mode with intensity oscillations observed in reflection high-energy electron diffraction. Films are of high structural quality, as documented by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The method should be suitable for the growth of other complex oxides containing ruthenium, opening up opportunities to investigate thin films that host rich exotic ground states.}, journal={APL Materials}, year={2017}, month={Sep} }
 @article{novel metal-insulator transition at the 
smtio3/srtio3
 interface_2017, url={http://dx.doi.org/10.1103/physrevlett.118.236803}, DOI={10.1103/physrevlett.118.236803}, abstractNote={We report on a metal-insulator transition (MIT) that is observed in an electron system at the SmTiO_{3}/SrTiO_{3} interface. This MIT is characterized by an abrupt transition at a critical temperature, below which the resistance changes by more than an order of magnitude. The temperature of the transition systematically depends on the carrier density, which is tuned from ∼1×10^{14} to 3×10^{14}  cm^{-2} by changing the SmTiO_{3} thickness. An analysis of the transport properties shows non-Fermi-liquid behavior and mass enhancement as the carrier density is lowered. We compare the MIT characteristics with those of known MITs in other material systems and show that they are distinctly different in several aspects. We tentatively conclude that both long-range Coulomb interactions and the fixed charge at the polar interface are likely to play a role in this MIT. The strong dependence on the carrier density makes this MIT of interest for field-tunable devices.}, journal={Physical Review Letters}, year={2017}, month={Jun} }
 @article{response of the lattice across the filling-controlled mott metal-insulator transition of a rare earth titanate_2017, url={http://dx.doi.org/10.1103/physrevlett.119.186803}, DOI={10.1103/physrevlett.119.186803}, abstractNote={The lattice response of a prototype Mott insulator, SmTiO_{3}, to hole doping is investigated with atomic-scale spatial resolution. SmTiO_{3} films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO_{3}-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. The results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed.}, journal={Physical Review Letters}, year={2017}, month={Nov} }
 @article{transparent and highly luminescent dysprosium- doped gdvo4 thin films fabricated by pulsed laser deposition_2017, url={http://dx.doi.org/10.1016/j.tsf.2017.07.069}, DOI={10.1016/j.tsf.2017.07.069}, abstractNote={Transparent, luminescent thin films of Dy3 +-doped GdVO4 were fabricated by pulsed laser deposition technique on quartz substrates. Thin film structure, morphology and optical properties were investigated and discussed in detail. X-ray analysis shows relatively intense reflection peaks confirming that as-deposited films are highly crystalline with strong (200) preferred orientation. Cross-sectional scanning electron microscopy shows relatively dense film with an average thickness of ~ 340 nm. Band gap of Dy3 +-doped GdVO4 thin film, estimated from diffuse reflectance spectrum, is 3.61 eV. Refractive index and extinction coefficient of thin films as a function of wavelength are extracted from ellipsometric spectra. The photoluminescent emission spectra have two dominant bands: one in the yellow (~ 573 nm, 4F9/2 → 6H13/2 transition) followed by the other in the blue (~ 484 nm, 4F9/2 → 6H15/2 transition) region resulting in the emission color placed in the white light region.}, journal={Thin Solid Films}, year={2017}, month={Sep} }
 @article{understanding the effects of a high surface area nanostructured indium tin oxide electrode on organic solar cell performance_2017, url={http://dx.doi.org/10.1021/acsami.7b10610}, DOI={10.1021/acsami.7b10610}, abstractNote={Organic solar cells (OSCs) are a complex assembly of disparate materials, each with a precise function within the device. Typically, the electrodes are flat, and the device is fabricated through a layering approach of the interfacial layers and photoactive materials. This work explores the integration of high surface area transparent electrodes to investigate the possible role(s) a three-dimensional electrode could take within an OSC, with a BHJ composed of a donor-acceptor combination with a high degree of electron and hole mobility mismatch. Nanotree indium tin oxide (ITO) electrodes were prepared via glancing angle deposition, structures that were previously demonstrated to be single-crystalline. A thin layer of zinc oxide was deposited on the ITO nanotrees via atomic layer deposition, followed by a self-assembled monolayer of C60-based molecules that was bound to the zinc oxide surface through a carboxylic acid group. Infiltration of these functionalized ITO nanotrees with the photoactive layer, the bulk heterojunction comprising PC71BM and a high hole mobility low band gap polymer (PDPPTT-T-TT), led to families of devices that were analyzed for the effect of nanotree height. When the height was varied from 0 to 50, 75, 100, and 120 nm, statistically significant differences in device performance were noted with the maximum device efficiencies observed with a nanotree height of 75 nm. From analysis of these results, it was found that the intrinsic mobility mismatch between the donor and acceptor phases could be compensated for when the electron collection length was reduced relative to the hole collection length, resulting in more balanced charge extraction and reduced recombination, leading to improved efficiencies. However, as the ITO nanotrees increased in height and branching, the decrease in electron collection length was offset by an increase in hole collection length and potential deleterious electric field redistribution effects, resulting in decreased efficiency.}, journal={ACS Applied Materials & Interfaces}, year={2017}, month={Nov} }
 @article{strain-induced electrostatic enhancements of bifeo3 nanowire loops_2016, url={http://dx.doi.org/10.1039/c6cp03068h}, DOI={10.1039/c6cp03068h}, abstractNote={Extraordinary electrostatic response has been found on electrospun BiFeO3nanowire loops by Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM).}, journal={Physical Chemistry Chemical Physics}, year={2016} }
 @article{structure and optical band gaps of (ba,sr)sno3 films grown by molecular beam epitaxy_2016, url={http://dx.doi.org/10.1116/1.4959004}, DOI={10.1116/1.4959004}, abstractNote={Epitaxial growth of (BaxSr1−x)SnO3 films with 0 ≤ x ≤ 1 using molecular beam epitaxy is reported. It is shown that SrSnO3 films can be grown coherently strained on closely lattice and symmetry matched PrScO3 substrates. The evolution of the optical band gap as a function of composition is determined by spectroscopic ellipsometry. The direct band gap monotonously decreases with x from to 4.46 eV (x = 0) to 3.36 eV (x = 1). A large Burnstein-Moss shift is observed with La-doping of BaSnO3 films. The shift corresponds approximately to the increase in Fermi level and is consistent with the low conduction band mass.}, journal={Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films}, year={2016}, month={Sep} }
 @article{ultra low density of interfacial traps with mixed thermal and plasma enhanced ald of high-κ gate dielectrics_2016, url={http://dx.doi.org/10.1039/c5ra26860e}, DOI={10.1039/c5ra26860e}, abstractNote={Anomalous growth per cycle was observed using in situ ellipsometry during the initial cycles of plasma enhanced atomic layer deposition of high-κ dielectrics, while thermal atomic layer deposition of these oxides exhibited linear growth per cycle.}, journal={RSC Advances}, year={2016} }
 @article{effect of chemical substitution on the morphology and optical properties of bi1−xcaxfeo3 films grown by pulsed-laser deposition_2013, url={http://dx.doi.org/10.1007/s10854-012-0724-7}, DOI={10.1007/s10854-012-0724-7}, journal={Journal of Materials Science: Materials in Electronics}, year={2013}, month={Jan} }
 @article{effect of simultaneous chemical substitution of a and b sites on the electronic structure of bifeo3 films grown on batio3/sio2/si substrate_2013, url={http://dx.doi.org/10.1007/s10854-013-1069-6}, DOI={10.1007/s10854-013-1069-6}, journal={Journal of Materials Science: Materials in Electronics}, year={2013}, month={Jun} }
 @article{conductor–insulator transition and electronic structure of ca-doped bifeo3 films_2012, url={http://dx.doi.org/10.1016/j.matlet.2012.05.126}, DOI={10.1016/j.matlet.2012.05.126}, abstractNote={The electronic conductor-insulator transition in Ca-doped BiFeO3 films grown by pulsed-laser deposition technique has been investigated. Nature of the transition is resolved to be Mott type through the control of band-filling. Calcium resolved to have colossal effect on enhancing the electrical conductivity of BiFeO3, but it did not affect band gap of the mother phase perceptibly. UV-visible study yielded band gap of 2.72-2.81 eV (at 300 K) for different concentrations of calcium. Both UV-visible and photoluminescence spectra revealed sub-band gap transitions at 2.17 and 2.38 eV, of which the latter might be ascribed to the oxygen vacancies.}, journal={Materials Letters}, year={2012}, month={Sep} }
 @article{electronic structure and morphological study of batio3 film grown by pulsed-laser deposition_2012, url={http://dx.doi.org/10.1016/j.matlet.2011.12.081}, DOI={10.1016/j.matlet.2011.12.081}, abstractNote={The morphological characteristics and electronic structure of the BaTiO3 films grown by pulsed-laser deposition technique have been investigated. AFM and FE-SEM images reveal columnar growth characteristic of these films. Utilizing spectrophotometer, optical band gap of the films were reckoned to be about 3.76 eV. Both dα/dE and PL vs. E plots reveal numerous luminance states in the gap. Despite the presence of many luminance faults in the gap, cations manage to preserve their electronic states.}, journal={Materials Letters}, year={2012}, month={Apr} }
 @article{synthesis of sodium tungsten oxide nano-thick plates_2012, url={http://dx.doi.org/10.1016/j.matlet.2012.05.106}, DOI={10.1016/j.matlet.2012.05.106}, abstractNote={In this letter a simple procedure to synthesize sodium tungsten oxide nano-thick plates from WO3 films has been reported. WO3 films were grown by pulsed-laser deposition method and then heat treated at temperatures up to 560 °C and times up to 120 min. Slide glass was used as both substrate and sodium source simultaneously. XRD analysis revealed presence of an amorphous structure for as-deposited WO3 films. On the other hand, XRD showed formation of a monoclinic WO3 structure with annealing in lower temperatures and a triclinic Na0.5WO3.25 structure with annealing at higher temperatures. Intensity of the triclinic phase peaks enhanced drastically by rising annealing temperature and time. SEM results depicted presence of Na0.5WO3.25 nano-thick plates with thickness of about 160 nm and width of about 3 μm. Finally, XPS analysis revealed that heat treatment temperature does not affect tungsten valence state.}, journal={Materials Letters}, year={2012}, month={Sep} }
 @article{the effect of dynamic strain aging on room temperature mechanical properties of high martensite dual phase (hmdp) steel_2012, url={http://dx.doi.org/10.1016/j.msea.2012.04.082}, DOI={10.1016/j.msea.2012.04.082}, abstractNote={AISI 4340 steel bars were heated at 900 °C for one hour, annealed at 738 °C for different durations and oil-quenched in order to obtain dual phase steels with different ferrite volume fractions. A 3% prestrain at the temperature range of 150–450 °C was then imposed to the samples, and room temperature tensile tests were carried out, afterwards. Results indicate that the maximum values for both yield and ultimate tensile strength would exist for the samples pre-strained at the temperature range of 250–300 °C. Also, a sudden drop of the ductility was observed at the mentioned temperature range. The observed behavior might be attributed to the occurrence of dynamic strain aging taken place at this temperature range. It was also shown that the ferrite volume fraction has not had any remarkable influence on the strength behavior of the samples, yet its increase was shown to have affected the work hardening behavior of the samples. Fractography analyses were also performed, showing the featureless fracture surface of the samples prestrain at the range of 250–300 °C, confirming the occurrence of dynamic strain aging at this condition.}, journal={Materials Science and Engineering: A}, year={2012}, month={Jul} }
 @article{effect of iron oxide and silica doping on microstructure, bandgap and photocatalytic properties of titania by water-in-oil microemulsion technique_2011, url={http://dx.doi.org/10.1080/0371750x.2011.10600173}, DOI={10.1080/0371750x.2011.10600173}, abstractNote={The microemulsion method was successfully used to prepare a series of TiO2, Fe oxide and SiO2 doped TiO2 nanoparticles at Fe/Ti atomic ratio of 10% and Si/Ti atomic ratio of 15%. The molar ratio of water to surfactant (W0) was 2. The samples were calcinated at 350°C. The structural features of TiO2, Fe oxide and SiO2-TiO2 were investigated by XRD, UV-Visible spectroscopy, SEM and TEM. XRD data verified the formation of typical characteristic anatase form in all the prepared Fe and SiO2-doped TiO2 samples. In comparison with the pure TiO2, Fe oxide and SiO2-TiO2 samples were relatively large in particle size, indicating that doping with Fe oxide and SiO2 can help in increasing the particle size. The role of SiO2 and Fe oxide doping could be related to the reduction in bandgap of the titania particles; this, in turn, could increase the ability of the particles in absorbing photons with energy in the visible spectrum. The doping of highly stabilized SiO2, Fe oxide in the titania matrix lead to the significant red shift of optical response towards visible light owing to the reduced bandgap energy. Among all the pure Fe and SiO2 doped TiO2, Fe oxide-TiO2 sample showed the highest activity of the photocatalytic decomposition of methylene blue (k = 2.1 × 10–2 min–1).}, journal={Transactions of the Indian Ceramic Society}, year={2011}, month={Oct} }
 @article{investigation of dark and light conductivities in calcium doped bismuth ferrite thin films_2011, url={http://dx.doi.org/10.1016/j.matlet.2011.06.052}, DOI={10.1016/j.matlet.2011.06.052}, abstractNote={Electrical conductivities in dark and light were investigated in Calcium doped Bismuth Ferrite thin films. Higher dark conductivity, in the order of 10 times higher than conductivity of bismuth ferrite, was observed for Bi0.85Ca0.15FeO3 − δ. Structural analyses using Rietveld refinement showed a deviation from volume reduction for Bi0.85Ca0.15FeO3 − δ which could be the reason of abnormally high conductivity for this compound. Although higher calcium doping reduced conductivity, photoconductivity was observed again. Atomic Force Microscopy investigations showed that surface roughness and grain size decreased with increasing calcium concentration. Enhanced photoconductivity is reported for Bi0.7Ca0.3FeO3 − δ with ~ 2.8 eV direct optical band gap at 300 K with surface roughness of ~ 2 nm.}, journal={Materials Letters}, year={2011}, month={Oct} }
 @article{photoconductivity and diode effect in bi rich multiferroic bifeo3 thin films grown by pulsed-laser deposition_2011, url={http://dx.doi.org/10.1007/s10854-010-0217-5}, DOI={10.1007/s10854-010-0217-5}, journal={Journal of Materials Science: Materials in Electronics}, year={2011}, month={Jul} }