Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X05: Topological Superconductivity: General II |
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Sponsoring Units: DMP Chair: Tay-Rong Chang, National Cheng Kung University Room: BCEC 108 |
Friday, March 8, 2019 8:00AM - 8:12AM |
X05.00001: Quasi 1D topological nodal superconducting vortex line state in doped 3D Dirac Semimetals Shengshan Qin, Lun Hu, Congcong Le, Jinfeng Zeng, Fu-Chun Zhang, Chen Fang, Jiangping Hu We study the vortex bound states in three dimensional (3D) Dirac semimetals with both time reversal symmetry and inversion symmetry. Assuming two Dirac points on the kz-axis and bulk s-wave superconductivity, the results turn out to be strongly anisotropic: if the vortex line is perpendicular to the kz-direction, the bulk |
Friday, March 8, 2019 8:12AM - 8:24AM |
X05.00002: Finite temperature topological states in a chain of magnetic adatoms on a superconductor Maciej Maska, Anna Gorczyca-Goraj, Tadeusz Domanski It is known that magnetic moments of a one-dimensional chain of adatoms on a superconductor self-organize into a spiral magnetic structure, which leads to topologically nontrivial superconductivity. Such a system can host the Majorana quasiparticles near its edges. The interaction between the localized moments is mediated by itinerant electrons. Upon tracing out the fermionic degrees of freedom, one obtains long range temperature-dependent effective interaction between the moments. Using Monte Carlo techniques we calculate the thermodynamic properties of the system. In particular, we demonstrate that with increasing temperature the correlation length of the magnetic order decreases, eventually driving the system to a topologically trivial phase. Using the simulated annealing method we also show, that at low temperature a phase separation can take place in the chain, where only part of the system is in the topologically nontrivial state and the rest of it is in the trivial state. |
Friday, March 8, 2019 8:24AM - 8:36AM |
X05.00003: Quantum Transport in Nanowires Grown via Template Assisted Selective Epitaxy and Contacted by an s-wave Superconductor M A Mueed, Benjamin Madon, Fabrizio Nichele, Markus Ritter, Noel Arellano, Heinz Schmid, Fenner Harper, Rahul Roy, Heike Riel, Aakash Pushp The hybrid system of an s-wave superconductor and a semiconducting nanowire with strong spin-orbit coupling (e.g. InAs, InSb) is a robust platform for realizing Majorana Fermion, a quasi-particle which is considered to be the building block for fault tolerant quantum computation. In our study, we prepare InAs nanowire networks using Template Assisted Selective Epitaxy (TASE) method and contact them using an s-wave superconducting material. The TASE method offers a reproducible way to grow high-quality nanowire in non-trivial device geometries, such as cross and Y- junctions, proposed for braiding operations of Majorana Fermions. Here, we present the quantum transport data measured on TASE-grown InAs nanowires with different device geometries. |
Friday, March 8, 2019 8:36AM - 8:48AM |
X05.00004: Enhanced Triplet Pairing in Magnetic Junctions with s-wave Superconductors Chenghao Shen, Thomas Vezin, Jong E Han, Igor Zutic A common path to Majorana fermions and topologically-protected quantum computing relies on spin-triplet superconductivity[1]. While spin-triplet pairing is elusive in nature and even common spin-triplet candidates, such as Sr2RuO4, could support alternative explanations[2], proximity effects in heterostructures can overcome these limitations. Specifically, a common expectation is that robust spin-triplet superconductivity in magnetic junctions should rely on highly spin-polarized magnets or complex magnetic multilayers[3]. Instead, we predict that the interplay of interfacial spin-orbit coupling and the barrier strength in simple magnetic junctions with s-wave superconductors can lead to nearly complete spin-triplet superconducting proximity effects when magnets have only a small spin polarization. We show that this enhanced spin-triplet regime is characterized by a huge increase in conductance magnetoanisotropy[4], orders of magnitude larger than in the normal state. |
Friday, March 8, 2019 8:48AM - 9:00AM |
X05.00005: Magnetic coupling between dopant atoms in superconducting doped topological insulators Cody Youmans, Areg Ghazaryan, Pouyan Ghaemi Doped topological insulators have been shown to exhibit unconventional superconducting phases where novel bound states can occur at defects such as vortices. Recent experimental studies on Niobium-doped Bismuth Selenide have shown that the magnetic properties of dopant atoms can strongly affect the resulting superconducting phase. This effect is mainly due to the development of Yu-Shiba-Rusinov bound-states at the magnetic atoms and the coupling of such states through the superconducting environment. In this talk, we show that the doping level can critically affect the type of magnetic coupling between dopant atoms in superconducting doped topological insulators and thereby influence their magnetic and superconducting properties. |
Friday, March 8, 2019 9:00AM - 9:12AM |
X05.00006: Superconductor Quasiparticles with Random Curvature, Robust Criticality, and T-Linear Resistivity Sayed Ali Akbar Ghorashi, Matthew Foster We study quenched random curvature disorder for 2D massless relativistic carriers. This describes a topological superconductor Majorana surface fluid with generic time-reversal invariant dirt. It should also apply to any non-topological Dirac or Majorana system in which the disorder is sufficiently smooth, as could be the case for d-wave quasiparticles in the cuprates with remote dopants. |
Friday, March 8, 2019 9:12AM - 9:24AM |
X05.00007: Majorana bound states in magnetic skyrmions imposed onto a superconductor Stefan Rex, Igor V. Gornyi, Alexander D. Mirlin We consider a two-dimensional superconductor exchange-coupled to the magnetic texture of a close-by chiral magnetic layer. In particular, we study how magnetic skyrmions can induce the formation of Majorana bound states (MBS) in the superconductor, where we focus on realistic skyrmions with winding number one. We show that MBS are supported if a vortex is pinned to the skyrmion core. In addition, we consider a chain of skyrmions, which may host MBS at its ends. In light of recent experimental progress on the manipulation of skyrmions, such systems are promising candidates to achieve direct spacial control of MBS. |
Friday, March 8, 2019 9:24AM - 9:36AM |
X05.00008: Development of the Scanning Majorana Microscope Eric Goodwin, Michael Gottschalk, Alex Levchenko, Stuart Holden Tessmer The Scanning Majorana Microscope (SMM) is being developed to provide novel ways for verification of the existence of Majorana zero modes. Inspired by a variety of scanning probe methods, the SMM consists of an aluminum quantum dot fabricated on the end of a sharp glass tip. By connecting the probe to an ultrasensitive charge-sensing circuit, the counting statistics of electrons entering the quantum dot can be characterized. It has been predicted theoretically that cases with and without Majorana coupling should exhibit qualitatively different full counting statistics of charge tunneling events despite the fact that differential linear conductance might have zero-bias features in both cases. Thus this microscope represents an important tool for detecting Majoranas going beyond existing experimental probes. Fabrication and preliminary measurements of the SMM will be presented. |
Friday, March 8, 2019 9:36AM - 9:48AM |
X05.00009: Local Andreev reflection induced by Chiral Majorana Fermions ZheShen Gao, Kam Tuen Law, Chui-Zhen Chen When superconductivity is proximity induced into a quantum anomalous system, it is predicted to host Chiral Majorana Edge Modes(CMEMs), which would induce a unique half quantized plateau as its transport signature. This was recently found in the experiments[Science 357, 294 (2017)]. However, it was argued that without superconductivity, disorder alone could also induce such signature. Thus more experimental evidence is called to determine whether superconductivity was the actual factor. Here we proposed to use local tunneling spectroscopy to directly probe the edge state of the hybrid system. We used Non-Equilibrium Green's Function to show that for topological phase with chern number N=±1/2 which hosts 1/2 CMEM would have a dip/plateau in differential conductance measurements respectively. Comparison with Thermal metal was also included. |
Friday, March 8, 2019 9:48AM - 10:00AM |
X05.00010: Erasing odd-parity states in a semiconductor quantum dot coupled to a superconductor Po Zhang, Hao Wu, Zhaoen Su, Rok Zitko, Eduardo Lee, Diana Car, Sébastien Plissard, Moira Hocevar, Sasa Gazibegovic, Roy Op het Veld, Ghada Badawy, Erik P. A. M. Bakkers, Sergey M Frolov Andreev bound states (ABS) exhibit many similarities to Majorana bound states (MBS). It would be of interest to study ABS in the system where MBS may emerge. The knowledge of ABS in a single dot is also crucial to understand more complicated systems, such as an artificial NbTiN /InSb dot chain that emulates a 1D Kitaev model. Here we study the erasing of odd-parity ABS in a quantum dot with gate-tunable superconducting coupling. The dot is defined in an InSb nanowire/NbTiN superconductor hybrid system. Fine gates are used to tune the coupling, the barrier and the chemical potential. In weak coupling regime, a parity-changing pattern of ABS is observed inside the Coulomb diamonds. In strong coupling regime, the ABS pattern opens a gap and the odd-parity regime is ‘erased’ from the pattern. We study this transition with different source-drain bias, map the phase boundary between even/odd states in magnetic fields and compare it to a finite-size Majorana nanowire. |
Friday, March 8, 2019 10:00AM - 10:12AM |
X05.00011: Observing pairs of zero-bias end states in three-terminal Superconductor-Semiconductor devices: Part I Denise Puglia, Gian-Luca Anselmetti, Gerbold Menard, Filip Malinowski, Esteban A Martinez, Joon Sue Lee, Sukgeun Choi, Mihir Pendharkar, Geoffrey C. Gardner, Sergei Gronin, Ray Kallaher, Michael Manfra, Chris Palmstrom, Charles M Marcus, Lucas Casparis, Andrew P Higginbotham Majorana zero-energy modes located at the ends of topological superconductors are an appealing platform for topological quantum computing. Zero-bias peaks (ZBPs) are ubiquitously observed in tunneling spectroscopy of hybrid superconductor-semiconductor nanowires, consistent with expectations for Majorana modes. However, the emergence of those zero-energy modes in pairs at the ends of 1D topological superconductors is a central -- and so far untested -- prediction. Enabled by recent materials breakthroughs in selective area growth (SAG), we demonstrate a platform for testing this prediction by probing the conductance matrix of a three-terminal InAs wire proximitized by Al. We introduce the measurement technique and study correlations of sub-gap states at zero field, finding evidence of localized states at the wire ends and delocalized bulk states. Correlated, zero-bias features emerging in finite field at both ends of the device will be presented in Part II. |
Friday, March 8, 2019 10:12AM - 10:24AM |
X05.00012: Andreev or Majorana, Cooper finds out Constantin Schrade, Liang Fu We study a Cooper pair transistor realized by a mesoscopic superconductor island that couples to a pair of s-wave superconducting leads. For a trivial island, the critical supercurrent between the leads exhibits a well-known 2e-periodicity in the island-gate charge. We show that for an island with spatially separated zero-energy Majorana or Andreev bound states the periodicity of the magnitude of the critical supercurrent transitions to 1e in the island-gate charge. Moreover, for Andreev bound states the current-phase relation displays a sign reversal when the parity of the charge ground state of the island changes between even and odd. Notably, for Majorana bound states the same sign reversal does not occur. Our results highlight the relevance of measuring the full current-phase relation of a Cooper pair transistor for clarifying the nature of zero-energy bound states in candidate systems for topological superconductors and provide an initial step towards integrating Majorana qubits in superconducting circuits. |
Friday, March 8, 2019 10:24AM - 10:36AM |
X05.00013: Power-law Temperature Dependence of the Penetration Depth in a Topological Superconductor due to Surface States Tsz Chun Wu, Hridis K Pal, Pavan Hosur, Matthew Foster We study the temperature dependence of the penetration depth in a 3D topological superconductor (TSC), incorporating the paramagnetic current due to the Majorana surface state. Bulk topological superconductors are predicted to host gapless 2D surface Majorana fluids, which are a promising platform for topological quantum computation. Here, we consider a model class DIII p-wave TSC and compute its response to an external magnetic field. Interestingly, in addition to the conventional London contribution to the Meissner effect coming from the bulk, our calculation shows that there is a non-trivial $T^{3}$ power law temperature dependence of the penetration depth due to the surface state in the low temperature limit. Our system is fully gapped in the bulk, and our result should be compared to bulk nodal superconductivity, which also exhibits power-law behavior. Our results imply that power-law temperature dependence of the penetration depth can be one indicator of topological superconductivity, in addition to the standard one-particle probes (STM, ARPES). |
Friday, March 8, 2019 10:36AM - 10:48AM |
X05.00014: Topological d+s wave superconductors in a multi-orbital quadratic band touching system GiBaik Sim, Archana Mishra, Moon Jip Park, Yong-Baek Kim, Gil Young Cho, SungBin Lee We will discuss generic realization of topological superconductivity in three dimensional quadratic band touching system. Based on the interacting Luttinger model, we exhibit that the absence of particle-hole symmetry leads the system to favor the special d-wave superconductors with parasitic s-wave pairings ; uniaxial nematic phase with parasitic s-wave pairing (d_(3z^2-r^2)+ s) and time reversal symmetry broken phase with parasitic s-wave pairing (d_(3z^2-r^2,xy)+id_(x^2-y^2)+s). (d_(3z^2-r^2)+ s) phase possess nodal rings with winding number \pm 2 and corresponding drumhead-like surface states. (d_(3z^2-r^2,xy)+id_(x^2-y^2)+s) phase contain Bogoliubov Fermi-pockets with Chern number \pm 2 and corresponding zero-energy arc states. We will also argue possible applications of our theory to several materials including half-heusler compound YPtBi and relevant future experiments. |
Friday, March 8, 2019 10:48AM - 11:00AM |
X05.00015: Observing pairs of zero-bias end states in three-terminal superconductor-semiconductor devices: Part II Esteban A Martinez, Denise Puglia, Gian-Luca Anselmetti, Gerbold Menard, Filip Malinowski, Geoffrey C. Gardner, Sergei Gronin, Ray Kallaher, Joon Sue Lee, Sukgeun Choi, Mihir Pendharkar, Chris Palmstrom, Michael Manfra, Charles M Marcus, Andrew P Higginbotham, Lucas Casparis Majorana zero-energy modes located at the ends of topological superconductors are an appealing platform for topological quantum computing. Zero-bias peaks (ZBPs) are ubiquitously observed in tunneling spectroscopy of hybrid superconductor-semiconductor nanowires, consistent with expectations for Majorana modes. However, the emergence of those zero-energy modes in pairs at the ends of 1D topological superconductors is a central -- and so far untested -- prediction. Enabled by recent materials breakthroughs in selective area growth (SAG), we demonstrate a platform for testing this prediction by probing the conductance matrix of a three-terminal InAs wire proximitized by Al. We perform tunneling spectroscopy independently on both ends of the wire as a function of longitudinal magnetic field and voltage. ZBPs emerge which are correlated and robust for these parameters. |
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