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Electrostatic control of quantum phases in KTaO3-based planar constrictions
Authors:
Jordan T. McCourt,
Ethan G. Arnault,
Merve Baksi,
Samuel J. Poage,
Salva Salmani-Rezaie,
Divine P. Kumah,
Kaveh Ahadi,
Gleb Finkelstein
Abstract:
Two-dimensional electron gases (2DEGs) formed at complex oxide interfaces offer a unique platform to engineer quantum nanostructures. However, scalable fabrication of locally addressable devices in these materials remains challenging. Here, we demonstrate an efficient fabrication approach by patterning narrow constrictions in a superconducting KTaO3-based heterostructure. The constrictions are ind…
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Two-dimensional electron gases (2DEGs) formed at complex oxide interfaces offer a unique platform to engineer quantum nanostructures. However, scalable fabrication of locally addressable devices in these materials remains challenging. Here, we demonstrate an efficient fabrication approach by patterning narrow constrictions in a superconducting KTaO3-based heterostructure. The constrictions are individually tunable via the coplanar side gates formed within the same 2DEG plane. Our technique leverages the high dielectric permittivity of KTaO3 (epsilon_r ~ 5000) to achieve strong electrostatic modulation of the superconducting 2DEG. Transport measurements through the constriction reveal a range of transport regimes: Within the superconducting state, we demonstrate efficient modulation of the critical current and Berezinskii Kosterlitz Thouless (BKT) transition temperature at the weak link. Further tuning of the gate voltage reveals an unexpectedly regular Coulomb blockade pattern. All of these states are achievable with a side gate voltage |V_SG| < 1 V. The fabrication process is scalable and versatile, enabling a platform both to make superconducting field-effect transistors and to study a wide array of physical phenomena present at complex oxide interfaces.
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Submitted 23 June, 2025;
originally announced June 2025.
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Superconductivity in tin telluride films grown by molecular beam epitaxy
Authors:
Antonio Gonzalez,
Samuel J. Poage,
Bernardo Langa, Jr.,
Deepak Sapkota,
Salva Salmani-Rezaie,
Shalinee Chikara,
Michael D. Williams,
David A. Muller,
Kasra Sardashti,
Kaveh Ahadi
Abstract:
The intersection of superconductivity and ferroelectricity hosts a wide range of exotic quantum phenomena. Here, we report on the observation of superconductivity in high-quality tin telluride films grown by molecular beam epitaxy. Unintentionally doped tin telluride undergoes a ferroelectric transition at ~100 K. The critical temperature of superconductivity increases monotonically with indium co…
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The intersection of superconductivity and ferroelectricity hosts a wide range of exotic quantum phenomena. Here, we report on the observation of superconductivity in high-quality tin telluride films grown by molecular beam epitaxy. Unintentionally doped tin telluride undergoes a ferroelectric transition at ~100 K. The critical temperature of superconductivity increases monotonically with indium concentration. The critical field of superconductivity, however, does not follow the same behavior as critical temperature with indium concentration and exhibits a carrier-density-dependent violation of the Pauli limit. The electron-phonon coupling, from the McMillan formula, exhibits a systematic enhancement with indium concentration, suggesting a potential violation of BCS weak coupling at high indium concentrations.
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Submitted 12 March, 2025;
originally announced March 2025.
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Violation of Pauli Limit at KTaO3(110) Interfaces
Authors:
Samuel J. Poage,
Xueshi Gao,
Merve Baksi,
Salva Salmani-Rezaie,
David A. Muller,
Divine P. Kumah,
Chun Ning Lau,
Jose Lorenzana,
Maria N. Gastiasoro,
Kaveh Ahadi
Abstract:
The superconducting order parameter at the KTaO3 interfaces and its dependence on interface orientation remains a subject of debate. The superconductivity at these interfaces exhibits strong resilience against in-plane magnetic field and violates Pauli limit. The interface orientation dependence of critical field and violation of Pauli limit, however, have not been investigated. To address this pr…
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The superconducting order parameter at the KTaO3 interfaces and its dependence on interface orientation remains a subject of debate. The superconductivity at these interfaces exhibits strong resilience against in-plane magnetic field and violates Pauli limit. The interface orientation dependence of critical field and violation of Pauli limit, however, have not been investigated. To address this problem, we grew epitaxial LaMnO3/KTaO3 heterostructures using molecular beam epitaxy. We show that superconductivity is extremely robust against the in-plane magnetic field. Our results indicate that the interface orientation, despite impacting the critical temperature, does not affect the ratio of critical field to the Pauli limiting field. These results offer opportunities to engineer superconductors which are resilient against magnetic field.
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Submitted 18 February, 2025;
originally announced February 2025.
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Enhanced Critical Field of Superconductivity at an Oxide Interface
Authors:
Athby H. Al-Tawhid,
Samuel J. Poage,
Salva Salmani-Rezaie,
Shalinee Chikara,
David A. Muller,
Divine P. Kumah,
Maria N. Gastiasoro,
Jose Lorenzana,
Kaveh Ahadi
Abstract:
The nature of superconductivity and its interplay with strong spin-orbit coupling at the KTaO3(111) interfaces remains 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 sup…
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The nature of superconductivity and its interplay with strong spin-orbit coupling at the KTaO3(111) interfaces remains 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 carrier density. We argue that spin-orbit coupling drives the formation of anomalous quasiparticles with vanishing magnetic moment, providing the condensate significant immunity against magnetic fields beyond the Pauli paramagnetic limit. These results offer design opportunities for superconductors with extreme resilience against magnetic field.
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Submitted 27 April, 2023;
originally announced April 2023.