Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E52: Topological Superconductivity: Topological Insulators and SemimetalsFocus Live
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Sponsoring Units: DMP Chair: Badih Assaf, University of Notre Dame |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E52.00001: Josephson Junctions in Topological Crystalline Insulators Invited Speaker: James Williams In this talk I will report on the properties of Josephson junctions fabricated with weak links of the topological crystalline insulator SnTe. Unexpectedly, these junctions exhibit anomalous DC and AC Josephson effects and magnetic diffraction patterns. The anomalies observed are consistent with a current-phase relation which breaks time reversal symmetry. The origin of this effect will be elucidated, demonstrating how the combination of the multiband proximity effect and the low-temperature ferroelectric distortion give rise to the observed time reversal symmetry breaking. Finally, I will discuss the importance of our results for the generation of Majorana bound states in superconducting topological crystalline insulators. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E52.00002: Searching for ideal topological crystalline insulators and topological superconductors in Pb-Sn-In-Te system Genda Gu, Ruidan Zhong, John Schneeloch, Qiang Li, Yangmu Li, Tonica Valla, Peter David Johnson, John Tranquada The discovery of 3D topological insulator materials and topological superconductor open up a new research field in the condensed matter physics. In order to search for the topological superconductor, we have grown a large number of the single crystals of Pb-system ( Pb-Sn-In-Te) topological crystalline insulator and their topological superconductor . We have measured the physical properties on these single crystals by various techniques. We have studied the effect of crystal growth condition, impurity and composition on the bulk electrical conductivity of these single crystals. We try to find out which composition and crystal growth condition is the best for the ideal topological insulator, topological crystalline insulator and topological superconductor |
Tuesday, March 16, 2021 8:48AM - 9:24AM Live |
E52.00003: Segmented Fermi surfaces: discovery and applications Invited Speaker: Michal Papaj Since the early days of Bardeen-Cooper-Schrieffer theory, it has been predicted that a sufficiently large supercurrent can close the energy gap in a superconductor and creates gapless Bogoliubov quasiparticles through the Doppler shift of quasiparticle energy due to the Cooper pair momentum. In such gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal state Fermi surface, while its remaining part is still gapped. In this talk I will discuss the recent discovery of such segmented Fermi surface in Bi2Te3 thin films proximitized by the superconductor NbSe2[1]. The observation is based on quasiparticle interference technique and supported by numerical modelling. I will then describe how the segmented Fermi surface can be used to induce a topological phase transition and create Majorana zero modes in quantum confined regions [2]. Our results reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum, and thus pave the way for further studies of states such as pair density wave and FFLO in unconventional superconductors. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E52.00004: Quantifying superconducting proximity pairing in topological (Bi1-xSbx)2Te3 films on niobium substrates Joseph Hlevyack, Sahand Najafzadeh, Meng-Kai Lin, Takahiro Hashimoto, Tsubaki Nagashima, Akihiro Tsuzuki, Akiko Fukushima, Cédric Bareille, Yen-Chen Tsui, Syu-You Guan, Wen-Yu Chen, Yang Bai, Peng Chen, Ro-Ya Liu, Yao Li, David Floetotto, José Avila, Sung-Kwan Mo, James Eckstein, Tien-Ming Chuang, Shik Shin, Kozo Okazaki, Tai-Chang Chiang Topological insulator films proximally coupled to simple isotropic superconductors are theoretically promising candidates for the 2D topological superconductor phase with exotic emergent phenomena, but fabricating these systems is often exceedingly difficult. By employing a novel cleavage-based “flip-chip” technique, we report the fabrication of single-crystalline (Bi1-xSbx)2Te3 thin films (x = 0 to 1) with predetermined layer thicknesses (2-10 layers) on superconducting Nb. While bulk conducting topological Bi2Se3 films interfaced with Nb films exhibit strong superconducting order in the nontrivial surface states, bulk insulating topological (Bi1-xSbx)2Te3 films on Nb (x = 0.62) instead show a massive suppression of proximity pairing at the surface, even for films only two layers in thickness. This giant attenuation of surface superconductivity is revealed by our recent ultrahigh-resolution band mappings and clarified by our ongoing scanning tunneling spectroscopy measurements, the results of which are compared with those of bulk conducting n-doped topological Bi2Se3/Nb and Bi2Te3/Nb. The results further highlight the design constraints of employing the superconducting proximity effect to generate topological superconductivity in nearly intrinsic systems. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E52.00005: Tunneling spectroscopy on Pb thin films on topological insulator Bi2Se3 Tadashi Machida, Katsuaki Sugawara, Yuhki Kohsaka, Takafumi Sato, Takao Sasagawa, Tetsuo Hanaguri A heterostructure of a topological insulator and an s-wave superconductor is a promising platform for topological superconductivity (TSC). Among the heterostructures developed so far, the surface of superconducting Pb grown on topological insulator TlBiSe2 is expected as an ideal system to detect a signature of TSC, since the TSC is exposed at the surface of Pb due to topological proximity effect [1]. However, it has been still unclear how the carrier doping and the bulk band affect its superconducting gap structure in such a system. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E52.00006: A two-dimensional analog of a doped Weyl superconductor Chiu Fan Bowen Lo, Hoi Chun Po, Andriy Nevidomskyy One route towards achieving topological superconductivity is to utilize the nontrivial topology associated with the Bloch states at the normal-state Fermi surfaces, as in the case of a doped Weyl semimetal. Here, we proposed a more general framework for relating the nontrivial band topology of the normal state Hamiltonian with the resulting superconductor within the weak-coupling mean-field description, which encompasses both the nodal and gapped topological cases. We showed that some of the known obstructions to getting a gapped superconductor could be readily interpreted within our framework, and also applied it to new symmetry classes. In particular, we discussed a concrete model of a nodal superconductor with an (effective) time-reversal symmetry, which could be viewed as a two-dimensional analog of a doped Weyl superconductor. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E52.00007: Three-dimensional time-reversal invariant topological superconductivity in doped chiral topological semimetals Yingyi Huang, Shao-Kai Jian Chiral topological semimetals host multifold degenerate band crossing points under the protection of crystalline symmetries. In this paper, we suggest the recently discovered chiral topological semimetals in space group P213 (No. 198), parts of which are superconducting upon doping, can be new candidates of time-reversal-invariant topological superconductors. By investigating the Fermi surfaces around the band crossing points, we clarify how the nontrivial topology of chiral topological semimetals affects their superconducting state and show the existence of topological superconductivity with surface Majorana fermions. We further demonstrate that the topological superconductivity is favored by inter-unit cell phonon-mediated electron-electron interaction. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E52.00008: Proximity Effect at the Superconductor-Topological Insulator Interface from First Principles Kyungwha Park, Gabor Csire, Balazs Ujfalussy A three-dimensional topological insulator (TI) film overlaid on an s-wave superconductor (SC) has emerged as one of good candidates for hosting a Majorana zero-mode at each vortex core in the proximity-induced topological SC state. Experiments on TI-SC heterostructures showed an intriguing range of proximity-induced SC gap sizes arising from TI bulk or topological surface states when the Fermi level lies in the TI bulk conduction band or in the topological surface state. Theoretical studies have been, so far, carried out based on effective models. Here we present the proximity-induced SC gap features, quasiparticle spectra, and effective TI pairing potential as a function of film thickness and chemical potential for Bi2Se3 films on SC PdTe, by solving the Bogoliubov-de Gennes equations within the screened Korringa-Kohn-Rostoker method in the framework of density-functional theory. We find multiple proximity-induced SC gaps where the gap sizes highly depend on characteristics of the TI states. The smallest gap arises from the topological surface state with its gap size depending on the TI pairing potential. Our results are compared to experiment. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E52.00009: Topological Monopole Superconductivity in Magnetically Doped Cd3As2 Eric Bobrow, David Vanderbilt, Yi Li We explore the monopole superconductivity arising from the proximity induced Cooper pairing in magnetically doped Dirac semimetal Cd3As2. Regardless of the details of proximity pairing, the zero-momentum inter-Fermi-surface pairing gap function is always nodal and described by monopole harmonic functions. It exhibits rich monopole pairing structure that depends on whether the Cooper pairing occurs between Fermi pockets with Chern numbers ±1 or ±2 at different chemical potentials. When Cooper pairing occurs between the Fermi pockets with Chern numbers ±1, the low-energy quasiparticle spectrum consists of linear BdG Weyl nodes, while for the pairing between Chern number ±2 Fermi pockets, the low-energy quasiparticle spectrum can exhibit quadratic BdG Weyl nodes near the Fermi surface along the four-fold rotation axis or linear BdG Weyl nodes away from the rotation axis. The total phase winding around all gap nodes on a Fermi pocket is a topological invariant proportional to the pair monopole charge. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E52.00010: Topological superconductivity in an interacting type-II Weyl model Peter Rosenberg, Efstratios Manousakis The discovery of superconducting Weyl semimetals has sparked an intense effort to understand the connection between topology and correlations in these materials, specifically, the pairing behavior of emergent Weyl fermions. Here we study the effect of attractive interactions in a simple Weyl model using a combination of numerically exact auxiliary-field quantum Monte Carlo calculations and mean-field theory. Our model describes a type-II Weyl system, inspired by the electronic structure of MoTe2, and we observe that the presence of extended interactions can give rise to topological superconducting states. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E52.00011: Fermi arc Criterion for Surface Majorana Modes in Superconducting Time-Reversal Symmetric Weyl-semimetals RAUF GIWA, Pavan R Hosur In recent years, many clever realizations of Majorana-fermions in condensed-matter have been predicted. Many have been verified by exploiting the interplay between superconductivity and band topology in metals and insulators. |
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