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 Y51: Topological Superconductivity: Pnictides and Heavy Fermion MaterialsLive
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Sponsoring Units: DMP Chair: Ady Stern, Weizmann Institute of Science |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y51.00001: Anomalous normal fluid response in chiral spin-triplet superconductor UTe2 Seokjin Bae, Hyunsoo Kim, Yun Suk Eo, Sheng Ran, I-Lin Liu, Wesley T Fuhrman, Johnpierre Paglione, Nicholas Butch, Steven M Anlage We report evidence of significant surface normal fluid response from a chiral spin-triplet pairing state of UTe2. The microwave surface impedance of UTe2 crystals was measured and converted to complex conductivity. The anomalous residual real part of conductivity in the zero temperature limit supports the presence of a significant normal fluid response in the ground state. The imaginary part of conductivity follows the low temperature behavior predicted for the axial spin-triplet state, which is further narrowed down to the chiral spin-triplet state with evidence of broken time-reversal symmetry [1]. The imaginary part of conductivity also reveals a low impurity scattering rate and low frequency-to-energy-gap ratio, implying that the observed normal fluid response is not due to an extrinsic origin. Candidate mechanisms such as a surface Majorana normal fluid, which is predicted for the chiral spin-triplet superconductor, will be discussed. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y51.00002: UTe2: a nearly insulating half-filled j=5/2, 5f3 heavy fermion metal. Alexander Shick, Shin-ichi Fujimori, Warren Pickett Correlated band theory implemented as a combination of |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y51.00003: Spontaneous Nernst effect in the iron-based superconductor Fe1+yTe1-xSex Lu Chen, Ziji Xiang, Colin B Tinsman, Bin Lei, Xianhui Chen, Genda Gu, Lu Li We present a study of the Nernst effect in an iron-based superconductor with a nontrivial band topology Fe1+yTe1-xSex . A nonzero Nernst signal is observed in a narrow temperature region around the superconducting transition temperature Tc at a zero field. This anomalous Nernst signal shows symmetric dependence on the external magnetic field and indicates an unconventional vortex contribution in an s-wave superconductor with a strong spin-orbit coupling, which is originated from the local magnetic moments of the interstitial Fe atoms. Our experiments also provide the first evidence of a locally broken time-reversal symmetry in bulk Fe1+yTe1-xSex single crystals. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y51.00004: Yu-Shiba-Rusinov states and chiral Majorana modes on an iron-based superconductor with a surface Dirac cone Ching-Kai Chiu, Ziqiang Wang Magnetic impurities on the surface of the superconductor lead to unusual low-energy physics. A magnetic adatom induces in-gap Yu-Shiba-Rusinov states. Particularly, for the s-wave superconductor possessing a surface Dirac cone, chiral Majorana modes emerge on the edge of the magnetic island. To establish the connection between Shiba and Majorana physics, we study the low-energy physics of the magnetic impurities on the surface of FeTexSe1−x with a Dirac cone. We show the evolution of the Yu-Shiba-Rusinov states and the transition to chiral Majorana modes as the Fe exchange coupling varies. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y51.00005: Topological transitions in a model for proximity-induced superconductivity Navketan Batra, Swagatam Nayak, Sanjeev Kumar Recent advancement in the theoretical understanding of triplet superconductivity has lead the researchers to believe in the technologically promising nature of p-wave superconductors. These superconductors have become a natural platform to look for non-abelian Majorana zero modes which can, in principle, be used to develop decoherence-free quantum computers. Although Strontium Ruthenate Sr2RuO4 and some Uranium based materials like UTe2 are possible candidates for a p-wave superconductor, a formal discovery of a p-wave superconductor awaits. Using a prototype model for proximity-induced superconductivity on a bilayer square lattice, we show that interlayer tunneling can drive change in topology of the Bogoliubov quasiparticle bands. Starting with topologically trivial superconductors, transitions to a nontrivial px+i py state and back to another trivial state are discovered. We characterize these phases in terms of edge-state spectra and Chern indices. We show that these transitions can also be controlled by experimentally viable control parameters, the bandwidth of the metallic layer, and the gate potential. Insights from our results on a simple model for proximity-induced superconductivity may open up a new route to discover topological superconductors. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y51.00006: Variation in LDOS for the Dirac surface states due to Se/Te composition fluctuations in FeTe0.55Se0.45 Tamoghna Barik, Jay Sau FeTe0.55Se0.45 is believed to be a strong topological phase for a narrow range of Te/Se composition as no evidences for non-trivial topology have been observed away from that specific composition. However, atomic-scale topographic image of the sample surface from STM shows in-homogeneity in Te/Se concentration with density correlation length of about 3 nm. The fluctuations in Te/Se composition can destroy the non-trivial topology locally and give rise to topological and trivial regions distributed across the sample. We investigate the effects of such topological-trivial phase boundaries in the sample on the Dirac surface state density distribution. With a minimal model for 3D strong TI, we tune the parameters to match the ARPES band structure and introduce disorder in the topology controlling parameter with correlation length of Te/Se density in-homogeneity. In particular, we study the variation of local density of states (LDOS) within the Dirac dispersion energy window that may be observed in LDOS measurement using STM within the energy window of Dirac dispersion. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y51.00007: Observation of magnetic adatom-induced Majorana vortex and its fusion with field-induced Majorana vortex in an iron-based superconductor Peng Fan, Fazhi Yang, Guojian Qian, Hui Chen, Yu-Yang Zhang, Geng Li, Zihao Huang, Yuqing Xing, Lingyuan Kong, Wenyao Liu, Kun Jiang, Chengmin Shen, Shixuan Du, John Schneeloch, Ruidan Zhong, Genda Gu, Ziqiang Wang, Hong Ding, Hongjun Gao Iron-based superconductors with nontrivial band topology have recently emerged as a surprisingly promising platform for creating distinct Majorana zero modes in magnetic vortices in a single material and at relatively high temperatures. Here we report the observation of the proposed quantum anomalous vortex with integer quantized vortex core states and Majorana zero mode induced by magnetic Fe adatoms deposited on the surface and the realization of its fusion with a nearby field-induced Majorana vortex in iron-based superconductor FeTe0.55Se0.45. We also observe vortex-free Yu-Shiba-Rusinov bound states at the Fe adatoms with a weaker coupling to the substrate, and discover a reversible transition between Yu-Shiba-Rusinov states and Majorana zero mode by manipulating the exchange coupling strength. The dual origin of the Majorana zero modes, from magnetic adatoms and external magnetic field, provides a new single-material platform for studying their interactions and braiding in superconductors bearing topological band structures. |
Friday, March 19, 2021 12:54PM - 1:06PM Not Participating |
Y51.00008: Local imaging of Thermal, magnetic and superconducting signals in FeTe1-xSex Yiftach Frenkel, Charles Zhang, Charles Tschirhart, Mason J Gray, Alex Potts, Liam Cohen, Andrea Young
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Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y51.00009: Boundary-Obstructed Topological High-Tc Superconductivity in Iron Pnictides Chaoxing Liu, Xianxin Wu, Wladimir Benalcazar, Yinxiang Li, Ronny Thomale, Jiangping Hu Nontrivial topology and unconventional pairing are two central guiding principles in the contemporary search for and analysis of superconducting materials and heterostructure compounds. It is quite rare that a single material compound possesses both non-trivial topological electronic band structure and unconventional pairing. In this work, we will describe an example of such system in iron-based superconductors. We propose to realize high-order topological superconductors, a new topological phase with the gapless modes located at the corner/hinge instead of the edge/surface, in the 112-family of iron pnictides, such as Ca1-xLaxFeAs2 [1], with the great advantage of the Curie temperature above 40K. Our theory provides the microscopic physical mechanism and topological characterization of this topological phase. Our works not only provide a physical understanding of the existing experiments, but also opens a new arena for high-order topological superconductivity with stable corner/hinge Majorana modes in intrinsic superconductors with high Curie temperature. |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y51.00010: Method for Readout of Majorana Parity in Topological Superconductors Using Magnetic Force Microscopy Benjamin November, Jay Sau, James Williams, Jenny E. Hoffman Recently, FeTexSe1-x has been shown to host Majorana zero-energy modes (MZMs) in topological superconducting vortex cores. Pairs of MZMs can potentially be used as topologically protected qubits. By applying a surface Fu-Kane model, we numerically calculate the wavefunction solution to the Bogoliubov-de Gennes equation for both a pair of spatially separated single vortices and the double vortex limit of complete overlap. We then compute the supercurrent generated by zero-energy mode splitting and the resulting magnetic field gradient above the surface. We conclude it is possible to measure the presence of this excess supercurrent, and thus the quantum state of the MZM pair, using magnetic force microscopy[1]. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y51.00011: Coexistence of high-temperature superconductivity and nontrivial topology in two-dimensional cobalt pnictide monolayers on SrTiO3 Jiaqing Gao, Wenjun Ding, Shunhong Zhang, Zhenyu Zhang, Ping Cui Among the iron-based superconductors, FeSe has been extensively studied for exploring the high transition temperature (Tc) superconductivity, as well as the exotic physics of Majorana states hosted in topological superconductors. Here we use first-principles approaches to identify a new class of isovalent and structurally identical counterparts of FeSe, namely, the monolayered CoX (X = P, As, Sb, Bi), which are not only promising candidates for realizing high-Tc superconductivity, but also offer new opportunity to study topological superconductivity. We demonstrate that, similar to the recently reported CoSb monolayer, the CoX (X = P, As, Bi) monolayers can adopt the FeSe-like layered structures and possess superconducting properties comparable with or superior to FeSe and CoSb, mainly attributed to the electronically isovalency nature of these systems. More strikingly, our further analyses show that all these four CoX monolayers possess nontrivial topological properties characterized by band inversions, odd Z2 invariants, and exhibition of topological edge states either in freestanding form or supported on SrTiO3. These findings can provide new platforms for exploring topological superconductivity in two-dimensional limit. |
Friday, March 19, 2021 1:42PM - 1:54PM On Demand |
Y51.00012: Magnetic, superconducting, and topological surface states on Fe1+yTe1−xSex Yangmu Li, Nader Zaki, David Michael Fobes, Zhijun Xu, Genda Gu, Rongwei Hu, Cedomir Petrovic, Andrei Savici, Vasile Garlea, Peter David Johnson, John Tranquada, Igor Zaliznyak The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in recent reports of topological surface superconductivity and Majorana zero modes. Here, we combine neutron scattering, angle-resolved photoemission spectroscopy, and microprobe composition and resistivity measurements to characterize the electronic state of Fe1+yTe1−xSex. We establish a phase diagram in which the superconductivity is observed only at sufficiently low Fe concentration, in association with distinct antiferromagnetic correlations, while the coexisting topological surface state occurs only at sufficiently high Te concentration. |
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