Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T27: Superconductivity:Devices & Materials-II |
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Sponsoring Units: DCMP Chair: Daniel Duong, University of South Carolina Room: Room 219 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T27.00001: Josephson diode effect in twisted d-wave superconductors Pavel Volkov, Tarun Tummuru, Marcel Franz, Jed Pixley, Stephan Plugge, Etienne Lantagne-Hurtubise Twisted d-wave superconductors near 45° twist are predicted to spontaneously break time-reversal symmetry due to cotunneling of Cooper pairs. We study emergent critical current non-reciprocity near 45° twist, which serves as a direct probe of time-reversal breaking. |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T27.00002: Josephson Diode Effect in Twisted Interface of Cuprate Superconductors Xiaomeng Cui, Pavel Volkov, Frank Zhao, Nicola Poccia, Hyobin Yoo, Rebecca Engelke, Yuval Ronen, Ruidan Zhong, Genda Gu, Stephan Plugge, Tarun Tummuru, Marcel Franz, Jedediah H Pixley, Philip Kim We report a tunable superconducting diode effect across the twisted cuprate Josephson junctions (JJs) near 45 degrees of twisting angle. The JJs are formed by twisted Van der Waals interfaces of two optimally doped Bi2Sr2CaCu2O8+x crystals assembled in a controlled environment. When the twisting angles are close to 45 degrees, we find the interfacial JJ coupled superconducting order parameter gains a nontrivial phase between the two layers. In these JJs, the second harmonic term becomes dominant in the current-phase relationship, leading to spontaneous time-reversal symmetry breaking. We observe the superconducting diode effect with non-reciprocal switching current distributions. The polarity of the diode can be switched by controlling the sweeping sequences of biasing current as the two TRS broken ground states can be selectively prepared according to resistively and capacitively shunted JJ model. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T27.00003: Theory of the persistent superconducting diode effect in twisted high-Tc cuprates Marcel Franz, Pavel Volkov, Etienne Lantagne-Hurtubise, Tarun Tummuru, Stephan Plugge, Jedediah H Pixley C-axis Josephson junctions fabricated from Bi2Sr2CaCu2O8+δ flakes twisted near 45° exhibit superconducting diode effect with a well-defined polarity which persists even after the sample has been cycled through the normal phase by raising its temperature or by exceeding its critical current. This observation suggests that time-reversal symmetry in these twisted flakes is broken not only below Tc, as suggested by existing theoretical work which predicts a chiral d+id' phase, but also in the normal state. We present here a symmetry-based phenomenological framework that explains the observed properties of such junctions with a minimal number of assumptions. Our model postulates an extra Ising order parameter that is linearly coupled to the superconducting chirality and remains ordered in the normal state -- thus providing the mechanism for the memory effect that underlies the fixed diode polarity. We show that, remarkably, this coupling is only symmetry-allowed in twisted junctions; at zero twist it vanishes in accord with the large body of experimental data indicating that untwisted optimally doped cuprates are non-magnetic. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T27.00004: Superconducting Diode Effect in a Three-terminal Josephson Device Mohit Gupta The phenomenon of non-reciprocal critical current in a Josephson device, termed Josephson diode effect, has garnered much recent interest. It is typically attributed to spin-orbit interaction and time reversal symmetry breaking in these systems. Here we report observation of the Josephson diode effect in a three-terminal Josephson device based upon InAs quantum well two-dimensional electron gas proximitized by epitaxial aluminum. We demonstrate that the diode efficiency can be tuned by a small out-of-plane magnetic field and electrostatic gating. We show that the diode effect in this device is a consequence of artificial realization of a current-phase relation that is non-2π-periodic. These Josephson devices may serve as gate tunable building blocks in designing topologically protected qubits. Furthermore, we show that the diode effect is an inherent property of multi-terminal Josephson devices. This establishes an immediately scalable approach by which potential applications of the Josephson diode effect can be realized, which is agnostic to the underlying material platform (arXiv:2206.08471v2). |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T27.00005: Diode effect in Josephson junctions with epitaxial trigonal tellurium tunnel barrier Varrick Suezaki, Daniel Morales, En-De Chu, Peng Wei Recently, the nonreciprocal phenomena in superconductors, such as the diode effect of supercurrent, has |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T27.00006: The gate-tuneable Josephson diode Nick van Loo, Grzegorz P Mazur, David van Driel, Jiyin Wang, Ghada Badawy, Sasa Gazibegovic, Erik P. A. M. Bakkers, Leo P Kouwenhoven Superconducting diodes are a recently-discovered quantum analog of classical diodes. The superconducting diode effect relies on the breaking of both time-reversal and inversion symmetry. As a result, the the critical current of a superconductor can become dependent on the direction of the applied current. The combination of these ingredients naturally occurs in proximitized semiconductors under a magnetic field. There, it is also predicted to give rise to exotic physics such as topological superconductivity. In this work, we use InSb nanowires proximitized by Al to investigate the superconducting diode effect. Through shadow-wall lithography, we create short Josephson junctions with gate control of both the junction as well as the proximitized leads. We identify two distinct physical mechanisms both leading to a superconducting diode effect. In the proximitized leads, a magnetic field perpendicular to the nanowire axis can be used to generate finite momentum cooper-pairing, which results in a maximum diode effect whenever the applied field is parallel to the spin-orbit direction. On the other hand, interference of multiple modes in the junction can also result in a finite diode effect, which occurs even when the field is applied parallel to the current flow in the nanowire. Both effects exhibit a strong dependence on the electrostatic gate voltages. This makes the semiconductor-superconductor hybrid Josephson diode the ideal element for innovative superconducting computation devices. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T27.00007: Ubiquitous Superconducting Diode Effect in Superconductor Thin Films Yasen Hou, Fabrizio Nichele, Hang Chi, Alessandro Lodesani, Yingying Wu, Markus Ritter, Daniel Haxell, Margarita Davydova, Stefan Ilic, Ourania Glezakou-Elbert, Amith Varambally, Sebastian Bergeret, Akashdeep Kamra, Liang Fu, Patrick A Lee, Jagadeesh S Moodera The macroscopic coherence in superconductors supports dissipationless supercurrent which could play a central role in emerging quantum technologies. Accomplishing unequal supercurrents in the forward and backward directions may be expected to enable unprecedented functionalities. This nonreciprocity of critical supercurrents is called superconducting (SC) diode effect. We demonstrate strong SC diode effect in conventional SC thin films, such as niobium and vanadium, employing external magnetic fields as small as 1 Oe. Interfacing the SC layer with a ferromagnetic semiconductor EuS, we further accomplish a non-volatile SC diode effect reaching a giant efficiency of 65%. By careful control experiments and theoretical modeling, we demonstrate that the critical supercurrent nonreciprocity in SC thin films could be easily accomplished with asymmetrical vortex edge/surface barriers and the universal Meissner screening current governing the critical currents. Our engineering of the SC diode effect in simple systems opens door for novel technologies while revealing crucial prerequisites for the search of exotic superconducting states harboring finite-momentum Cooper pairing. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T27.00008: Giant Superconducting Diode Effect from Controlled Edge Asymmetry Amith Varambally, Ourania-Maria Glezakou-Elbert, Yasen Hou, Akashdeep Kamra, Patrick A Lee, Jagadeesh S Moodera Superconducting thin film strips displaying a polarity-dependant critical current, superconducting diode rectification behavior, can be controlled via a small magnetic field. This could serve as an energy-efficient building block for digital circuit logic, similar to semiconductor diodes. Both the Meissner screening effect and symmetry breaking of the two edges in a given superconducting thin film were found to be necessary for V superconducting films to display the rectification. Edge defects achieve vortex pinning as well as the current crowding effect, both of which influence diode efficiency. In previous studies, edge symmetry breaking was not controlled, and was unavoidable in the fabrication process. Edge symmetry can be broken by modulating via engineered edge geometry. We aimed to control the asymmetry of the two edges in V superconducting thin films by patterning rectangular indentations on only one of the two edges. This allowed us to more than double diode efficiency in pure superconductor thin films (with diode efficiency reaching 40%), opening the door for further improvement in creating highly efficient superconductor diodes. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T27.00009: Ideal gas law-like behavior in chemically-induced superconductors Shermane M Benjamin, Brian W Casas, Paul M Eugenio, Olatunde Oladehin, William L Nelson, Ryan E Baumbach Fruitful attempts at understanding superconductors has led to the discovery of numerous empirical relationships concerning their physical properties. This includes, for example, the BNC empirical scaling rule [1], ΔC ~ Tc3, for some iron pnictide superconductors. Where ΔC represents the jump in heat capacity at critical temperature Tc3 . Similar scaling behaviors exist for superconductors in general as well. To date, however, the link between superconductivity and the chemical/structural properties of materials remains poorly understood. Here we report empirical ideal gas law-like relationships between the chemical unit and physical structure of chemically induced superconductors near the onset of superconductivity. [2] |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T27.00010: Designing high-Tc bulk and two-dimensional (2D) superconductors with BCS-inspired screening, density functional theory, deep-learning and experiments Kamal Choudhary, Daniel Wines, Kevin F Garrity, Adam Biacchi, Francesca Tavazza High-throughput density functional theory (DFT) calculations allow for a systematic search for conventional Bardeen–Cooper–Schrieffer (BCS) superconductors. With the recent interest in bulk and two-dimensional (2D) superconductors, we develop a multi-step workflow for the discovery of conventional superconductors. After screening over 55,000 bulk and 1,000 2D materials in the JARVIS-DFT database, we perform electron-phonon coupling (EPC) calculations and use the McMillan-Allen-Dynes formula to calculate the superconducting transition temperature (Tc) for 1,736 bulk and 172 2D materials. From this, we identify several bulk and monolayer structures that are dynamically stable with superconducting transition temperatures above 5 K, including bulk materials such as VTe, KB6, Ru3NbC, V3Pt, ScN, LaN2, RuO2, and TaC and 2D materials such as W2N3, NbO2, ZrBrO, TiClO, NaSn2S4, Mg2B4C2 and the previously undiscovered Mg2B4N2, which has a Tc of 22.51 K. Additionally, we demonstrate that deep-learning models can predict superconductor properties, including the Eliashberg function, thousands of times faster than direct first principles computations for bulk materials. Finally, we performed experiments to determine the Tc of selected layered superconductors (2H-NbSe2, 2H-NbS2, ZrSiS, FeSe) and discuss the measured results within the context of our DFT computed results. We aim that the outcome of this workflow can guide future computational and experimental studies of new and emerging superconductors by providing a roadmap of high-throughput DFT data. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T27.00011: Engineering Chiral Topological Superconductivity in Twisted Ising Superconductors Xiaodong Hu, Ying Ran Van der Waals materials like NbSe2 or TaS2 have demonstrated Ising superconductivity down to atomically thin layers. Due to the spin-orbit coupling, these superconductors have the in-plane upper critical magnetic field far beyond the Pauli limit. We theoretically demonstrate that, twisted bilayer Ising superconductors separated by a ferromagnetic buffer layer can naturally host chiral topological superconductivity with Chern numbers, which can be realized in heterostructures like NbSe2/CrCl3/NbSe2. Under appropriate experimental conditions the topological superconducting gap can reach >0.1 meV, leading to readily observable signatures such as the quantized thermal Hall transport at low temperatures. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T27.00012: Interfacial Magnon-Mediated Superconductivity in Twisted Bilayer Graphene Bjørnulf Brekke, Arne Brataas, Asle Sudbø The interfacial coupling between electrons and magnons in separate adjacent layers can mediate an attractive electron-electron interaction and induce superconductivity. We consider magic-angle twisted bilayer graphene sandwiched between two ferromagnetic insulators to optimize this effect. As a result, magnons induce a multicomponent superconducting state characterized by p-wave symmetry. Furthermore, estimates for the critical temperature are significantly higher than for the intrinsic mechanism due to the enhanced density of states at the magic angle. Our results open a new path for exploring magnon-induced superconductivity. |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T27.00013: Non-reciprocity in low-symmetry superconductors Yuli B Lyanda-Geller, Jukka Vayrynen, Ananthesh Sundaresh, Leonid P Rokhinson On the time-reversal and spatial symmetry grounds, the noncentrosymmetric superconductors can exhibit the supercurrents, superconducting diode and non-reciprocity effects of an intrinsic origin. The currents in an equilibrium vanish in a simply connected superconductors or normal metals. Even when the external current flows, the Lifshits invariants linear in the Cooper pair momentum cannot result in non-reciprocity in uniform superconductors. We derive the nonreciprocity effects due to intrinsic spin-orbit and Zeemann coupling microscopically at low temperatures and near the critical temperature and demonstrate their origin in superconductors with low symmetry. The linear Rashba and Dressselhaus interactions in the electorn spectrum result in the odd-power terms of higher order in the Cooper pair momentum in the Cooperon/Fluctuations propagator in the presence of the magnetic Zeemann coupling.The odd-power terms result in nonreciprocity in the critical current and kinetical inductance. The cubic in momentum Dresselhaus terms in the electron spectum also contribute to nonreciprocity. The presence of Dresselhaus- and Rashba-induced contributions to non-reciprocity result in strong anisotropy of nonreciprocal signals, particularly in proximitized noncentrosymmetric materials. |
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