@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{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{ozbek_brooks_zhang_al-tawhid_stoica_zhang_kumah_2022, title={Superconducting phase of TixOy thin films grown by molecular beam epitaxy}, volume={6}, ISSN={["2475-9953"]}, url={https://doi.org/10.1103/PhysRevMaterials.6.064805}, DOI={10.1103/PhysRevMaterials.6.064805}, abstractNote={We investigate the complex relationship between the growth conditions and the structural and transport properties of ${\mathrm{Ti}}_{x}{\mathrm{O}}_{y}$ thin films grown by molecular beam epitaxy. Transport properties ranging from metallicity to superconductivity and insulating states are stabilized by effectively tuning the O/Ti ratio via the Ti flux rate and the O partial pressure ${P}_{\mathrm{O}x}$ for films grown on $(0001)\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates at ${850}^{\ensuremath{\circ}}$ C. A cubic $c\text{\ensuremath{-}}{\mathrm{TiO}}_{1\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$ buffer layer is formed for low O/Ti ratios, while a corundum $\mathrm{cr}\text{\ensuremath{-}}{\mathrm{Ti}}_{2}{\mathrm{O}}_{3}$ layer is formed under higher-oxidizing conditions. Metallicity is observed for $c\text{\ensuremath{-}}{\mathrm{TiO}}_{1\ensuremath{-}\ensuremath{\delta}}$ buffer layers. The superconducting $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Ti}}_{3}{\mathrm{O}}_{5}$ Magn\'eli phase is found to nucleate on a $c\text{\ensuremath{-}}{\mathrm{TiO}}_{1\ensuremath{-}\ensuremath{\delta}}$ buffer for intermediate ${P}_{\mathrm{O}x}$ conditions, and an insulator-superconducting transition is observed at 4.5 K $({\mathrm{T}}_{C}^{\mathrm{onset}}=6K)$ for 85 nm thick films. Strain relaxation of $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Ti}}_{3}{\mathrm{O}}_{5}$ occurs with increasing film thickness and correlates with a thickness-dependent increase in ${T}_{C}$ observed for ${\mathrm{Ti}}_{x}{\mathrm{O}}_{y}$ thin films.}, number={6}, journal={PHYSICAL REVIEW MATERIALS}, author={Ozbek, Yasemin and Brooks, Cooper and Zhang, Xuanyi and Al-Tawhid, Athby and Stoica, Vladmir A. and Zhang, Zhan and Kumah, Divine P.}, year={2022}, month={Jun} }
 @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{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} }