Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N21: Unconventional SuperconductivityFocus Recordings Available

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Sponsoring Units: DMP Chair: Kaveh Delfanazari, University of Glasgow, UK Room: McCormick Place W185D 
Wednesday, March 16, 2022 11:30AM  12:06PM 
N21.00001: Magnetic, superconducting, and topological surface states on FeTeSe Invited Speaker: Igor A Zaliznyak The idea of employing nonAbelian statistics for errorfree quantum computing ignited interest in reports of topological surface superconductivity. Recently, topological surface state and Majorana zero modes (MZMs) were detected on "11" Febased superconductor FeTe_{0.55}Se_{0.45}. However, these properties are not observed uniformly across the sample surface. Scanning tunneling spectroscopy experiments detect coexisting vortices with and without MZM, as well as an inhomogeneous bulk superconductivity. The understanding and practical control of these electronic inhomogeneities present a prominent challenge for potential applications of topological superconductivity. 
Wednesday, March 16, 2022 12:06PM  12:18PM 
N21.00002: Signatures of emergent interfacial superconductivity in 45degree twisted van der Waals Cuprate Superconductors Alex cui, Shu Yang Frank Zhao, Pavel A Volkov, Jed Pixley, Nicola Poccia, Philip Kim, Genda Gu, Ruidan Zhong, Sangmin Lee, Hyobin Yoo, Jules A Gardener, Austin Akey, Rebecca Engelke, Yuval Ronen, Marcel Franz, Tarun Tummuru, Stephan Plugge We developed a cryogenic assembly technique to fabricate Josephson Junctions with an atomically sharp twisted interface between Bi2Sr2CaCu2O8+x crystals. Transport measurements probing the interface revealed a suppressed but finite critical current close to 45 degrees. Fraunhofer patterns revealed anomalous junction effective thickness, which can be explained by a theoretical analysis that incorporates the second harmonic in the Josephson Energy versus phase relation. We study the change of Fraunhofer patterns as we vary applied inplane magnetic field direction, probing the current distribution in the Josephson junction. Our theoretical analysis supports the dominant second harmonic in our Josephson Junctions, indicating timereversal broken interfacial superconductivity. 
Wednesday, March 16, 2022 12:18PM  12:30PM 
N21.00003: Probing the Josephson effect in twisted nodal superconductors Pavel A Volkov, Jed Pixley, Philip Kim, Alex cui, Shu Yang Frank Zhao, Nicola Poccia Motivated by the recent proposals for unconventional emergent physics in twisted bilayers of nodal superconductors, we study the Josephson effect at the twisted interface between dwave superconductors. We demonstrate that the critical current can exhibit a nonmonotonic temperature dependence with a maximum at a nonzero temperature as well as a complex dependence on the twist angle at low temperatures. Effects of interface inhomogeneity are also discussed and demonstrated that they can drive topological to trivial superconducting transitions. Close to 45 degree twist we find that the critical current does not vanish due to Cooper pair cotunneling, which leads to a strong second harmonic in the currentphase relation and a putative transition to a timereversal breaking topological superconducting phase. We show how the behavior of critical current in a magnetic field and under microwave drive can yield unambiguous evidence of Cooper pair cotunneling. 
Wednesday, March 16, 2022 12:30PM  12:42PM 
N21.00004: Fraunhofer Spectra in Monopole Superconductor Josephson Junctions Grayson R Frazier, Junyi Zhang, Junjia Zhang, Yi Li Monopole superconductors arise from the nontrivial Berry phases of Cooper pairs which fundamentally change the corresponding superconducting gap function from the familiar description using s, p and d wave symmetry to exotic monopole harmonic symmetry. Because the U(1) phase of the pairing order cannot be well defined globally over an entire Fermi surface, we study the phase sensitive Fraunhofer patters in models of Josephson junctions between monopole superconductors and between a monopole superconductor and an swave superconductor using a gauge invariant description. When a magnetic field is applied to the junction, the interplay among the shifts in Cooper pair momentum and the thickness of the junction barrier gives rise to the zero patterns in the Fraunhofer spectra distinguishing from, for example, chiral pwave superconductor Josephson junctions. 
Wednesday, March 16, 2022 12:42PM  12:54PM 
N21.00005: Quantum phase diagram and topological superconductivity by doping Mott insulators on the triangular lattice Yixuan Huang, Donna Sheng Understanding the emergence of unconventional superconductivity by doping Mott insulators and its interplay with conventional orders remains a major challenge in condensed matter physics. In this work we study the extended tJ model with threespin chiral interactions and establish the quantum phase diagram based on large scale Density Matrix Renormalization Group simulations. With increasing next nearest neighbor hopping (t') and Heisenberg spin exchange (J'), we identify both $d+id$wave topological superconducting state and extended dwave topologicallytrivial superconducting state, by the topological spin Chern number and pairing symmetry. Through proper bonddimension scaling, we find that the superconducting correlations demonstrate dominant quasilongranged order on wider cylinders, which may lead to different superconducting states in the 2D limit. Our results suggest that the $d+id$wave topological superconductivity can be induced by either doping a chiral spin liquid or magnetic ordered state as the hole dynamics plays an essential role in the dopinginduced topological phase transition, which provides new insights for the experimental discovery of unconventional topological superconductivity. 
Wednesday, March 16, 2022 12:54PM  1:06PM 
N21.00006: Quantum Geometry And OffDiagonal LongRange Order In Multiband Superconductor Guodong Jiang, Yafis Barlas

Wednesday, March 16, 2022 1:06PM  1:18PM 
N21.00007: A Universal Way to Engineer the Electronic Properties of Hybrid Devices. Guang Yang, Jiayu Shi, Degui Qian, Guoan Li, Michal Nowak, Paweł Wójcik, Erik P. A. M. Bakkers, Jie Shen The hybrid devices of superconductor and semiconductor nanowire (NW) with strong spinorbit interaction (SOI) can be driven to topological regime and host Majorana zero modes (MZMs), which are the building blocks of a topological computer. Here we fabricate hybrid devices with thick/thin Al/Pb film. By well controlling the etching time, we can modify the band bending strength of interface and control the electronic properties. This is demonstrated by that the AlInSb devices with different etching time shows quantized plateaus with varying number of modes. Moreover, high transmission of channels got by fitting the multiple Andreev reflection also proves the high quality of interface. In the thin PbNW devices, we observed gate tunable induced hard superconducting gap from 0 to ~1.4meV, with a suppression of conductance by three orders of magnitude. The effective gfactors, calculated through the evolution of states as a function of magnetic field, are remarkably large, e.g. several tens or even more than one hundred. This indicates the orbital effect and the strong SOI of Pb film. With the combination of pronounced enhancement of induced superconducting gap and gfactor, PbNW provides a better platform than AlNW for searching for MZMs, as well as constructing topological qubit. 
Wednesday, March 16, 2022 1:18PM  1:30PM 
N21.00008: Bound quasiparticle transport along the edges of superfluid ^{3}He Dmitry Zmeev, Samuli Autti, Ash Jennings, Richard Haley, George R Pickett, Malcolm Poole, Roch Schanen, Arkady A Soldatov, Viktor Tsepelin, Jakub Vonka, Vladislav V Zavjalov Superfluid ^{3}HeB in a container naturally consists of two virtually isolated systems: the threedimensional bulk of the superfluid, and a twodimensional surface layer of Andreevbound fermions. We discovered how to drive the bound fermions out of equilibrium and expel them into the bulk, where they can be observed [1]. Here we show that the quasiparticles not energetic enough to escape to bulk flow diffusively across macroscopic distances along the surface, demonstrating nonlocal dynamics that conserve energy and momentum. Similar twodimensional confinement of electrons at a low temperature has led to the discovery of a variety of quantum Hall phases. Our work thus opens a research outlook ranging from Majorana fermions to composite objects between bound quasiparticles and topological defects or bosonic bulk excitations. 
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