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 K42: Topological Superconductivity in Van Der Waals MaterialsFocus
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Sponsoring Units: DMP Chair: Suyang Xu, Harvard University Room: Room 318 |
Tuesday, March 7, 2023 3:00PM - 3:36PM |
K42.00001: Topological superconductivity realizations in 2D material system Invited Speaker: Yuval Ronen As two indistinguishable elementary particles interchange their positions, a fundamental property of their nature is revealed, their exchange statistics. This property gives rise to the Pauli exclusion principle of fermions, or the Bose-Einstein condensation of bosons. In the field of condensed-matter physics, governed by many-body interactions, novel exchange statistics may manifest in the emergence of different quantum phases. Of particular interest is the non-abelian exchange statistics, emanating from unconventional phases featuring topological superconductivity. |
Tuesday, March 7, 2023 3:36PM - 3:48PM Author not Attending |
K42.00002: Spectroscopic evidence for topological band structure in FeTe0.55Se0.45 Yingfei Li FeTe0.55Se0.45 (FTS) occupies a special spot in modern condensed matter physics at the intersections of electron correlation, topology, and unconventional superconductivity. The bulk electronic structure of FTS is predicted to be topologically nontrivial thanks to the band inversion between the dxz and pz bands along Γ-Z. This in turn would give rise to a Dirac surface state (DSS) hosting topological superconductivity below the bulk superconducting temperature. However, whether this prediction is indeed realized in FTS remains controversial in recent angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS) studies. In ARPES experiments, a Dirac-cone-like feature has been identified, yet only at certain out-of-plane momenta (kz), leading to speculations that it might originate from a bulk band instead of the DSS. Moreover, the measured band structure differs significantly from the density functional theory (DFT) predictions, with no direct observations of either the pz band or the bulk band inversion. Here we resolve this debate through a comprehensive ARPES investigation. We first observe a persistent DSS independent of kz. Then, by comparing FTS with FeSe which has no band inversion along Γ-Z, we identify the spectral weight fingerprint of both the presence of the pz band and inversion between the dxz and pz bands. Our results highlight the impact of strong correlation and large spin-orbit coupling in FTS and make a strong case for the existence of topological band structure in this unconventional superconductor. |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K42.00003: π-junction induced by strong inter-pocket transmission at FeTe.55 Se.45(FTS) half-shift domain wall Tamoghna Barik, Jay D Sau Recent scanning tunneling spectroscopy(STS) along crystalline domain walls (DWs) associated with a half unit cell shift have revealed sub-gap density of states that are expected to arise from helical Majorana modes. Such propagating Majorana modes have been proposed to exist on the surface state of topological materials similar to FTS along line defects where the superconducting order parameter (OP) is phase shifted by π. Here we propose a mechanism for the emergence of such a π shift in the OP across the half unit-cell shift DW of FTS. Our mechanism relies on the s± pairing symmetry across Γ and M pockets of FTS. We construct a tight binding model for the FTS mono-layer including the Fe-3dx2-y2 and 3dxz/yz orbitals and use the KWANT package to solve the scattering problem across the DW. The resultant inter-pocket transmission between Γ and M pockets is found to be typically larger than the intra-pocket transmissions. In parallel, calculation of the Bogoliubov de Gennes(BdG) spectra for the cases of π and 0-junctions at DW shows that the occupied levels have lower energy for the π-junction. We find that the latter calculation often favors a π-shift across the DW when an incoming electron of Γ(M) pocket, due to stronger inter-pocket transmission found in the former calculation, is Andreev reflected as a hole of M(Γ) pocket, which has opposite sign for the OP. We discuss parameter regimes where this mechanism might explain the STS experiments as well as propose to test this explanation by searching for evidence of large inter-pocket scattering. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K42.00004: Topological Superconductivity in Twisted Superconductors of Finite Thickness Kevin P Lucht, Pavel Volkov, Jedediah H Pixley Twisted bilayers of nodal superconductors have been predicted to host topological states under the application of interlayer supercurrent. Experimentally it is, however, more practical to twist superconducting flakes of finite thickness, containing several layers each. We consider a system of one monolayer dx2-y2 superconductor stacked with a twist on top of a N-layer flake. Under application of c-axis supercurrent through the system, we find that a topological gap opens in the bulk of the system with gapless edge modes. While the gap value decreases with N, the Chern number increases as |C| = 2(N+1). We discuss the dependence of the results on the interlayer tunneling strength, as well as signatures of the topological superconducting state in the thermal Hall conductance and local density of states, measurable in STM experiments. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K42.00005: Magnetic field-induced topological domains in twisted nodal superconductors Pavel Volkov, Jed Pixley, Justin H Wilson, Kevin P Lucht Topological phases have been predicted to emerge in twisted bilayers of nodal superconductors with time-reversal symmetry broken either spontaneously or by applying current. Here we study the quasiparticle spectrum in the presence of an in-plane magnetic field generating a Josephson vortex lattice. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K42.00006: Evidence of a two-component order parameter in 4Hb-TaS2 in the Little-Parks effect Avior Almoalem, Irena Feldman, Michael Shlafman, Yuval E Yaish, Mark H Fischer, Michael Moshe, Jonathan Ruhman, Amit Kanigel Finding unambiguous evidence of non-trivial pairing states is one of the greatest experimental challenges in the field of unconventional superconductivity. Such evidence requires phase-sensitive probes susceptible to the internal structure of the order parameter. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K42.00007: Superconductivity in Few-Layer Td-MoTe2 Damien Bérubé, Jian Tang, Vicky Hasse, Chandra Shekhar, Anyuan Gao, Siyuan Ding, Yu-fei Liu, Jian-Xiang Qiu, Houchen Li, Christian Tzschaschel, Thao H Dinh, Zhe Sun, Claudia Felser, Qiong Ma, Suyang Xu Layered transition metal dichalcogenides have recently emerged as promising candidates to explore the interplay between symmetry and novel quantum properties. Among them, bulk Td-MoTe2 is a type-II Weyl semimetal with low symmetry and a superconductive phase below 120 mK. In the 2D limit, few-layer Td-MoTe2 may feature topological superconductivity and display other exotic superconducting properties. In this talk, I will discuss electronic properties of few-layer Td-MoTe2, including an unusual gate dependence of the superconductivity that we have systematically characterized at multiple sample thicknesses. We supplement these intriguing transport results with optical measurements such as second harmonic generation. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K42.00008: Twisted Moire bilayer physics in square-lattice surfaces of time-reversal symmetric topological superconductors Ching-Kai Chiu, Fan Cui, Congcong Le, Qiang Zhang, Xianxin Wu Twisted bilayer graphene brings the flat energy bands from the Dirac cones serving as a new playground for strong correlations and topological phases. Beyond the hexagonal lattice, we study the physics of the twisted bilayer in the square lattice and focus on the scattering between the nodal points at M points in each layer. In particular, we consider the surface of time-reversal symmetric topological superconductors as a layer. Different from twisted bilayer graphene, time reversal symmetry and particle-hole symmetry protect the entire energy bands from separation in the Moire ´ Brillouin zone. We show that different ordered nodal points on the surface evolve to different types of flat bands with and without magic angles. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K42.00009: The effects of coupling Kagome superconductor CsV3Sb5 with a s-wave superconductor Bingzheng Han, Stephan Kim, Phuan Ong, Ni Ni, Tiema Qian, Xianhui Chen, Jianjun Ying We report the effects of coupling a Kagome superconductor CsV3Sb5 with an external s-wave superconductor. We prepared nanodevices from exfoliated CsV3Sb5 crystals with niobium (Nb) electrodes (Tc sim 8 K). The proximitized edge mode was manifested as periodic modulations of critical current in the differential resistance spectra dV/dI of the devices at varying applied biases I and fields muH. [1] Surprisingly, the period of modulations exceeded what corresponded to the physical area by a factor of four and remained consistent throughout. Moreover, cuts of the differential resistance spectra at zero bias exhibited antihysteric changes of resistance, a signature of incompatibility between two superconducting condensates probed through edge mode. [2] |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K42.00010: Josephson Junctions of Nodal Superconductors: Role of Spin-orbit coupling Ranjani Seshadri, Maxim Khodas, Dganit Meidan A monolayer transition metal dichalcogenide (TMD) such as niobium diselenide (NbSe2 ) exhibits unique superconducting properties. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K42.00011: Strain-enhanced superconductivity in topological Weyl semimetal MoTe2 Arfan Sewaket, Xinxin Cai, Tara Pena, Ahmad Azizimanesh, John Nichol, Stephen M Wu Recently, there have been reports of the existence of a superconducting edge state in Td-MoTe2, a topologically non-trivial type-II Weyl semimetal and intrinsic superconductor. Magnetic-field dependent oscillations in edge state critical current similar to the periodic oscillations observed in the Little-Parks experiment have been shown [1]. However, oscillatory features were only observed at ultralow temperature (20 mK) and in exfoliated flakes of 60-120 nm thickness, limiting the exploration of possible exotic topological properties of the superconducting edge states in more complex device configurations. Here, we show strain-induced Tc enhancement in MoTe2 by depositing stressed thin films onto flakes (process-induced strain engineering), where Tc is increased from 100 mK to >1.8 K in 5-10 nm thick flakes of MoTe2. We observe similar edge state oscillatory features, with an increase in the number of oscillatory modes and periods, all sustained to higher temperatures (>400 mK). These results lead us to suspect that strain may be used to tune edge state superconductivity alongside the expected enhancement of bulk Tc. |
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