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 S57: Topological Superconductor Materials: Modeling and Characterization MethodsFocus Live
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Sponsoring Units: DMP Chair: Ulrich Welp, Argonne National Laboratory |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S57.00001: Tunable Majorana networks based on second-order topological superconductors Alessio Calzona, Songbo Zhang, Bjoern Trauzettel Second-order topological superconductors (SOTSs) host localized Majorana fermions and represent a novel platform to study and exploit the properties of these non-Abelian anyons. We propose a way to realize networks based on SOTSs which allow to nucleate and braid Majorana bound states (MBSs) in an all-electrical manner, without fine-tuning. The proposed setups are scalable and can accommodate any even number of MBSs. Moreover, the MBSs in the networks allow defining qubits whose states can be initialized and read out by measuring Josephson currents flowing between SOTS islands. Our proposal can be implemented, for example, in monolayers of FeTe1−xSex, monolayers of 1T’-WTe2, and inverted Hg(Cd)Te quantum wells in proximity to conventional superconductors |
Thursday, March 18, 2021 11:42AM - 11:54AM Live |
S57.00002: Signatures of anisotropic topological superconductivity in a dc-SQUID Baris Pekerten, Benjamin S Hawn, Joseph Pakizer, Alex Matos Abiague We investigate the emergence of topological superconductivity (TS) in a dc-SQUID and its signatures on the ground state phase and critical current. The topological phase transition in each of the two planar Josephson junctions are individually tuned by using top gates. We specifically consider the cases when none, either or both junctions are in the topological regime. The coexistence of Rashba and Dresselhaus spin-orbit couplings leads to crystalline anisotropic TS. We theoretically show that the distinctive anisotropic effects on the ground state phase and critical current could be used for experimentally identifying topological phase transitions in the dc-SQUID. |
Thursday, March 18, 2021 11:54AM - 12:06PM Live |
S57.00003: Majorana conductance quantization in the presence of momentum relaxation processes Chaitrali Duse, Praveen Sriram, Bhaskaran Muralidharan Hybrid systems with proximity-induced superconductivity in semiconductor nanowires with spin-orbit coupling in a Zeeman field are a promising platform for hosting Majorana bound states (MBSs). In this work, we examine whether the quantized zero-bias conductance peak is robust enough to dephasing and momentum relaxation to remain a tell-tale signature of MBSs. We employ the Keldysh non-equilibrium Green’s function (NEGF) formalism to model quantum transport through the Majorana nanowire in an NSN setup. As expected, in the clean and phase-coherent limit, MBSs give rise to a quantized zero-bias peak (ZBP) in differential conductance, dominated by the local Andreev reflection. However, in the presence of phase and momentum relaxing interactions [1], we show that this ZBP signature is suppressed and does not remain quantized. For nanowires with short phase coherence lengths, such processes can render the ZBP indistinguishable from noise even in the presence of topological MBSs in the local density of states. Thus, we suggest that in Majorana nanowire experiments with scattering and relaxation effects, the absence of a quantized ZBP in conductance measurements does not necessarily preclude the existence of Majorana states. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S57.00004: Competing time scales and their experimental signatures in dissipative 1D Kitaev chain Yang Chao, Bo Yang Using the Lindblad master equation formalism, we study the oscillation of Josephson current in coupled Kitaev chains with the a dissipative boundary. In the super operator representation,the ac Josephson current is calculated in both the topological trivial and nontrivial phases. Different periodicities can be observed with different time scales determined by the energy scales of the applied voltage. If the voltage is small compared to the bulk and edge states dissipation rate, we will see a 2pi periodic current in both the topological trivial and nontrivial phase. By increasing the voltage so that so that the relevant time scale is larger than the edge dissipation rate, we can see a 4pi oscillating current in the topological phase. At large voltage when the period of ac current is much smaller than the time scale of correlation propagating from the junction to the boundary, a 4pi current can be seen in both the topological and trivial phase. Interestingly, the 4pi Josephson current in the trivial phase is induced by the chemical potential gradient of the reservoir with no analogy in equilibrium systems. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S57.00005: Many-body Quantum Geometry in Superconductor-Quantum Dot Chains Raffael Klees, Juan Carlos Cuevas, Wolfgang Belzig, Gianluca Rastelli Multiterminal Josephson junctions constitute engineered topological systems in arbitrary synthetic dimensions defined by the superconducting phases. Microwave spectroscopy enables the measurement of the quantum geometric tensor, a fundamental quantity describing both the quantum geometry and the topology of the emergent Andreev bound states in a unified manner. In this work we propose an experimentally feasible multiterminal setup of N quantum dots connected to N+1 superconducting leads to study nontrivial topology in terms of the many-body Chern number of the ground state. Moreover, we generalize the microwave spectroscopy scheme to the multiband case and show that the elements of the quantum geometric tensor of the noninteracting ground state can be experimentally accessed from the measurable oscillator strengths at low temperature. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S57.00006: Second Chern Number and Non-Abelian Berry Phase in Topological Superconducting Systems Hannes Weisbrich, Raffael Klees, Gianluca Rastelli, Wolfgang Belzig Topology ultimately unveils the roots of the perfect quantization observed in complex systems. The 2D quantum Hall effect is the celebrated archetype. Remarkably, topology can manifest itself even in higher-dimensional spaces in which control parameters play the role of extra, synthetic dimensions. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S57.00007: Tunable topological states hosted by unconventional superconductors with adatoms Andreas Kreisel, Timo Hyart, Bernd Rosenow Chains of magnetic atoms, placed on the surface of s-wave superconductors, have been established as a laboratory for the study of Majorana bound states. In such systems, the breaking of time reversal due to magnetic moments gives rise to the formation of in-gap states, which then hybridize to form one-dimensional topological superconductors. However, in unconventional superconductors even non-magnetic impurities can induce in-gap states since scattering of Cooper pairs changes their momentum but not their phase. Here, we propose a realistic path for creating topological superconductivity, which is based on an unconventional superconductor with a chain of non-magnetic adatoms on its surface. The system can be driven into a topological phase by tuning the magnitude and direction of an external Zeeman field, such that Majorana zero modes at its boundary can be generated, moved, and fused, paving the way towards braiding of Majorana zero modes. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S57.00008: Chiral Dirac Superconductors: Second-order and Boundary-obstructed Topology Apoorv Tiwari, Ammar Jahin, Yuxuan Wang We analyze the topological properties of a chiral p + ip superconductor for a two-dimensional |
Thursday, March 18, 2021 1:06PM - 1:42PM Live |
S57.00009: Predictive Discoveries of 2D Materials for Topological Superconductivity and High-Tc Superconductivity Invited Speaker: Zhenyu Zhang The recent discovery of topological materials as a new form of quantum matter offers appealing schemes for potential definitive realization of topological superconductors and unambiguous detection of Majorana fermions. In this talk, I will attempt to give an overview on the recent advances and latest excitements in this vibrant area, with some of our own stories surrounding low-dimensional topological superconductors and a new class of high-Tc superconductors squeezed in. Our first line of examples is on systems that rely on proximity effects; here we will show that proper introduction of dilute magnetic dopants at the interfaces of topological insulators and conventional superconductors can effectively convert the systems into chiral topological superconductors. Next we focus on intrinsic systems, exploring how Rashba spin-orbit coupling and van Hove singularity could join force to induce exotic topological phase transitions within the context of “correlation of correlations”. Beyond such microscopic model studies, we will also use first-principles approaches to identify candidate systems that promise to materialize 2D topological superconductivity. In doing so, we will highlight the importance of interfacial growth science and improved understanding of superconductivity mechanisms in guiding predictive discoveries of new high-Tc superconductors and topological superconductors. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S57.00010: Chiral Majorana hinge modes on curved surface with magnetic impurities Ilyoun Na, Luca Chirolli We discuss possible physical realizations of higher-order odd-parity topological superconductors (TSCs) starting with a time-reversal-invariant TSC (class DIII) on a three-dimensional sphere geometry. We construct such phases by introducing time-reversal and inversion symmetry breaking mass terms, that can be engineered with a magnetic field and magnetic impurities on the surface. We show that the RKKY interaction between magnetic impurities on a curved geometry promotes a ferromagnetic radial order due to the Ising properties of Majorana surface fermions, that competes with the external magnetic field. Using the RKKY interaction with dense enough magnetic impurities, we determine the optimal magnetic field to minimize orbital effects and enable the mass term which is odd under inversion and energetically favorable compared to a spherically symmetric hedgehog configuration. The resulting mass term will gap out the surface leaving a gapless one-dimensional chiral Majorana mode along inversion symmetric line on the surface, thus implementing a second-order TSC. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S57.00011: First-, second- and third-order topological superconductivity protected by point-group symmetries zhongyi zhang, Chen Fang The rich variety of crystalline symmetries of solids greatly enhance tenfold-way classes. Topological crystalline superconductors (TSC) are potential to host first-, second- and third-order topological states with protected surface, edge, and corner Majorana gapless modes. In this work, we establish a complete classification of first-, second- and third-order anomalous surface state in DIII class by stacking multiple copies of first-order states with different winding numbers on suitably chosen surface geometries. We find that under the given symmetry setting of normal state and of the pairing order parameter, there is a global obstruction to achieve a fully gapped surface, which leads to helical Majorana mid-gap modes that propagate along 1-D curves or are localized at some points on the surface. We analyze cases in all 32 point groups and give the "root states" that generate such anomalous surface state upon stacking. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S57.00012: Hole-Binding in Nx2 Dice-Ladder Rahul Soni, Gonzalo Alvarez, Elbio Dagotto Recent theoretical work has showed that the geometrical transition from 2D planes to quasi-1D ladders does not alter the basic topological properties in dice lattices. Additionally, interaction studies via DMRG and Lanczos for Nx2 ladders has revealed the existence of a ferrimagnetic phase in these systems at half filling [1]. In this work, we show the presence of negative binding energy for a pair of holes in this ferrimagnetic region of the Nx2 ladder. We will be discussing the dominant pair-pair correlation channels and compare with the charge and spin correlation channels. We will also discuss the structure of the one-hole and two-hole ground states in the Nx2 ladder system. Our efforts pave the way for exploring the presence of superconducting channels in such topological systems, where the combined effect of topology and correlation unveils rich physical aspects. |
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