Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K65: Topological Superconductors: Theory IIRecordings Available

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Sponsoring Units: DCMP Chair: Victor Vakaryuk, Physical Review Room: Hyatt Regency Hotel Grant Park C 
Tuesday, March 15, 2022 3:00PM  3:12PM 
K65.00001: Proposal for Majorana modes without a magnetic field in phasebiased Joesphson trijunction HuanKuang Wu, Jay D Sau We present a proposal for a phasebiased Josephsonjunctionbased Majorana system without an applied magnetic field. Such applied magnetic fields tend to degrade topological superconducting devices by suppressing superconductivity. Our proposal is similar to promising work that has already been demonstrated in phasebiased Josephson junctions in HgTe quantum wells. We show that in such a system, it is possible to eliminate the external magnetic field by introducing a third superconductor on the other side of the quantum well. We will discuss how this configuration hosts Majorana zero modes at the ends of the well following a similar mechanism to that in topological insulators as proposed by Fu and Kane. We demonstrate this idea by simulation with realistic experimental parameters and picking HgTe as the candidate junction material. 
Tuesday, March 15, 2022 3:12PM  3:24PM 
K65.00002: Signatures of Topological Superconductivity in the Spin Susceptibility of Josephson Junctions Alex MatosAbiague, Joseph D Pakizer We theoretically investigate how the spin susceptibility of a planar Josephson junction is affected when the system transits into the topological superconducting state. We show that the magnetic flux and magnetic field dependence of the spin susceptibility closely maps the phase diagram of the system. In the absence of an external magnetic flux the system can selftune into the topological superconducting state by minimizing its free energy. Selftuned topological transitions are accompanied by sharp peaks in the spin susceptibility, which can therefore be used as measurable fingerprints for detecting the topological superconducting state [1]. Away from the peaks, the amplitude of the spin susceptibility can provide qualitative information about the relative size of the topological gap. The signatures in the spin susceptibility are robust, even in junctions with narrow superconducting leads, where critical current minima may no longer serve as an indication of topological phase transitions [1]. The predicted results could be particularly relevant for future experiments on realization and detection of the topological superconducting state in planar Josephson junctions. 
Tuesday, March 15, 2022 3:24PM  3:36PM 
K65.00003: Quality factor for the quantization of zerobias conductance peaks in Majorana nanowire YiHua Lai, Jay D Sau A zerobias conductance peak (ZBCP) with a nearly quantized height of 2e^{2}/h is one of the most direct and unique signatures of a topological Majorana zero mode. However, despite recent experimental progress in observing large zero bias peaks, theoretical work has raised questions about the uniqueness of quantized ZBCPs as a signature for Majorana modes. On the other hand, the ZBCPs associated with Majorana modes are predicted, to be robustly quantized even as the tunnel barrier is pinched off to vanishingly low conductance. In this work we compare the robustness of the quantization of ZBCPs associated with Majorana modes, quasiMajoranas and disorder to variations of the tunnel barrier and Zeeman field. By defining a quality factor associated with the variation of the tunnel barier and Zeeman field for each type of ZBCP, we find that Majoranas are significantly more robust compared to nonMajorana ZBCPs in the ideal low temperature limit. However the distinction between Majoranas and nontopological ZBCPs is reduced at more practical temperatures such as 20mK. Based on the quality factors calculated over a wide range of parameters and models we conclude that the observation of a tunnel barrier quality factor over a threshold value of two might be considered a strong evidence of Majorana modes. 
Tuesday, March 15, 2022 3:36PM  3:48PM 
K65.00004: Higherorder topology and corner triplon excitations in twodimensional quantum spindimer models Arijit Haldar, Arun Paramekanti, Geremia Massarelli The concept of free fermion topology has been generalized to ddimensional phases that exhibit (dn)dimensional boundary modes, such as zerodimensional (0D) corner excitations. Motivated by recent extensions of these ideas to magnetic systems, we consider 2D quantum paramagnets formed by interacting spin dimers with dispersive triplet excitations. We propose two examples of such dimer models, where the spingapped bosonic triplon excitations are shown to host bands with nontrivial higherorder topology. We demonstrate this using realspace Bogoliubovde Gennes calculations that reveal the existence of nearmidbandgap corner triplon modes as a signature of higherorder bulk topology. We provide an understanding of the higherorder topology in these systems via a computation of bulk topological invariants as well as the construction of edge theories, and study their phase transitions as we tune parameters in the model Hamiltonians. We also discuss possible experimental approaches for detecting the emergent corner triplon modes. 
Tuesday, March 15, 2022 3:48PM  4:00PM 
K65.00005: Topological properties of nodal superconductors Ranjani Seshadri, Dganit Meidan, Maxim Khodas Monolayer and fewlayer transition metal dichalcogenides (TMDs) have been 
Tuesday, March 15, 2022 4:00PM  4:12PM 
K65.00006: Transport signatures of Floquet Majorana modes in Josephson junctions Rekha Kumari, Babak Seradjeh, Arijit Kundu We theoretically study the transport signature of unpaired Floquet Majorana edge modes in the Josephson current in weakly linked, periodically driven topological superconductors. In certain cases, similar to the case for static unpaired Majorana edge modes, we find that the Josephson current involving Floquet Majorana modes also shows a $4\pi$periodic nature. At this limit, the current is also linearly dependent on the coupling between superconductors. We match our numerical results using Floquet Green’s function technique with analytical expressions for the current, the occupation of the Floquet bands, and a perturbative analysis of the quasienergies. 
Tuesday, March 15, 2022 4:12PM  4:24PM 
K65.00007: Fresh look on finitesize effects in Majorana nanowires Rodrigo d Dourado, Carlos Egues, Poliana H Penteado The quest for the elusive Majorana zero mode (MZM) has puzzled theorists and experimentalists since its conception. In this work, we aim at investigating Kitaev  modeled nanowires and elucidating some misconceptions. Here we study finitesize effects in the presence of disorder and smoothconfining potentials. We numerically diagonalize the BdG Hamiltonian and explore different sets of parameters. In addition, we use the Green functions method to calculate the conductance. Our results show the emergence of MZMs in a preferred parameter regime, which may guide future experiments. 
Tuesday, March 15, 2022 4:24PM  4:36PM 
K65.00008: Z4 parafermionic edge modes in an interacting periodically driven topological superconductor Raditya W Bomantara I theoretically present a means to generate Z_{4} parafermion edge modes without fractional quantum Hall systems or complicated interactions. My proposal only requires a few simple ingredients, i.e., pwave superconductivity, magnetic field, fermionic Hubbard interaction, and periodic driving, all of which are compatible with current technology. I further show that the obtained parafermions, which can be analytically derived at special parameter values, have no static counterpart and arise from the interplay between an interaction effect and periodic driving. Strong numerical evidence suggests that these exotic quasiparticles are robust against variations in parameter values and spatial disorder. My construction not only serves as an excellent starting point for topological quantum computing beyond Majorana fermions, but also provides an intuitive mechanism of nonequilibrium quantum manybody phases. 
Tuesday, March 15, 2022 4:36PM  4:48PM 
K65.00009: Majorana fusion rules in a singlecharge topological transistor Ruben Seoane Souto, Martin Leijnse By now, there has been a lot of evidence of the existence of Majorana fermions at the ends of topological superconductors, hosting Majorana bound states (MBSs) at theis ends [1]. A demonstration of the theoretically predicted nonabelian properties of MBSs would constitute a definite proof of a topological superconducting phase, paving the way towards future topological quantum computing. Alongside the nontrivial braiding statistics, the fusion rules are fundamental properties of all nonabelian anyons. 
Tuesday, March 15, 2022 4:48PM  5:00PM 
K65.00010: Desining $\mathbb{Z}_2$ and $\mathbb{Z}_2 \times \mathbb{Z}_2$ topological orders using networks of Majorana bound states Mehdi Kargarian, Fatemeh Mohammadi The topologically protected ground states against local perturbations and nontrivial braiding statistics of quasiparticles provide a unique platform for topological quantum computations. However, the experimental realization of topologically ordered states in a controlled way has remained elusive notwithstanding huge attempts in the last few decades. 
Tuesday, March 15, 2022 5:00PM  5:12PM 
K65.00011: Equivalence of interacting semimetals and lowdensity manybody systems to singleparticle systems with quenched disorder Shijun Sun, Sergey Syzranov Describing collective behaviour of a large number of interacting particles is one of the biggest challenges in physics and is key to understanding phase transitions and transport and thermodynamic properties in systems with strong particle correlations. We demonstrate that a broad class of interacting disorderfree systems, such as nodal semimetals (e.g. graphene, Weyl, nodalline semimetals) and dilute interacting gases, can be mapped to noninteracting systems with quenched disorder. The interacting systems that allow for such a mapping include systems with a small singleparticle density of states at the chemical potential (e.g. near the nodal point or a nodal line in a topological semimetal), which leads to a suppressed screening of the interactions. The established duality suggests a new approach for analytical and numerical studies of manybody phenomena in a class of interacting disorderfree systems by reducing them to singleparticle problems. It allows one to predict, describe and classify manybody phenomena by mapping them to the effects known for disordered noninteracting systems. We illustrate the mapping by showing that clean semimetals with attractive interactions exhibit interactiondriven transitions at low temperatures in the same universality classes as the nonAnderson disorderdriven transitions predicted in highdimensional noninteracting semimetals. Furthermore, we find a new nonAnderson disorderdriven transition dual to a previously known interactiondriven transition in clean bosonic gases. The established principle may also be used to classify and describe phase transitions in dissipative systems described by nonHermitian Hamiltonians. 
Tuesday, March 15, 2022 5:12PM  5:24PM 
K65.00012: Dynamical protocols to improve majoranas and distinguish from trivial zero modes I. Brett Min, Bastien Fajardo, Tami PeregBarnea, Kartiek Agarwal In [2], a protocol was proposed for dynamically decoupling [1] imperfect (overlapping) Majorana Zero Modes (MZMs) via periodic double braiding of MZMs from a nanowire and a weakly coupled quantum dot. We further develop the protocol proposed in [2] which better suppresses the hybridization of MZMs. We also examine the consequences for tunneling conductance measurements in the presence of these dynamical protocols and argue that the conductance measurements are not ideal in differentiating MZMs from trivial Andreev Bound States (ABSs). Instead, we propose a new experimental scheme using these dynamical protocols to distinguish MZMs from trivial ABSs using qubit decoherence measurements. 
Tuesday, March 15, 2022 5:24PM  5:36PM 
K65.00013: Dynamical protocols to improve majoranas and distinguish from trivial zero modes II. Bastien Fajardo, Brett Min, Kartiek Agarwal, Tami PeregBarnea We discuss using the dynamical protocols proposed in Ref. [1], to distinguish between majorana zero modes and trivial bound states. The dynamical protocols can be shown to suppress lowfrequency noise, both from quasiparticle poisoning, and dephasing. The latter in particular is expected to play an important role in determining the properties of majorana zero modes realized in onedimensional wires. We demonstrate using analytical arguments and numerically, that decoherence due to dephasing noise is strongly suppressed in case when the wire features majorana zero modes but has no effect in the case of Andreev Bound States. We thus anticipate that such protocols could be used as better tests of the presence of majorana zero modes as opposed to tunneling conductance measurements. 
Tuesday, March 15, 2022 5:36PM  5:48PM 
K65.00014: Phases of a holographic model for multiWeyl semimetal Rodrigo A Soto Garrido, Vladimir Juricic, Ignacio Salazar Landea Holographic models for gapless Weyl and multiWeyl semimetals have been recently proposed in the literature. In this talk we will show that a holographic model for multiWeyl semimetals features a rather rich landscape of phases. Of particular interest is a novel phase that we call "xy nematic condensate". We demostrate that this phase is stable at strong coupling as we show by a free energy and a quasinormal mode analysis. In addition, we characterize this phase through the anomalous transport coefficients. We believe that our results could motivate future research in holographic realizations of the topological phases. 
Tuesday, March 15, 2022 5:48PM  6:00PM 
K65.00015: Topological Superconductivity in a Weyl model of stacked SuSchriefferHeeger chains Efstratios Manousakis, Peter Rosenberg In a previous publication, using quantum Monte Carlo and meanfield theory, we had studied conventional superconductivity in a Weyl system of stacked SuSchriefferHeeger (SSH) chains. In the present paper, we study a Weyl model of stacked SSH chains by introducing a simple and natural pairing term which couples different sublattices. We find topological superconductivity featuring Majorana states along the boundary perpendicular to the direction of the SuSchriefferHeeger dimerization. 
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