Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H05: Topological Superconductivity: 2D, JunctionsFocus
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Sponsoring Units: DMP Chair: Adrian Feiguin, Northeastern University Room: BCEC 108 |
Tuesday, March 5, 2019 2:30PM - 3:06PM |
H05.00001: Emergent two-dimensional superconductivity in few-layer stanene Invited Speaker: Ding Zhang The two-dimensional crystalline superconductors possess a variety of exotic properties such as the Griffiths singularity, the quantum metal phase as well as the strongly enhanced in-plane critical field [1]. Here we report the discovery of superconductivity in few layer stanene—ultrathin gray tin (111)—and the complete phase diagram in the magnetic field and temperature plane. The emergence of superconductivity in stanene is unexpected. Bulk gray tin is non-superconductive [1] and stanene attracts attention mostly because of its topological properties. Instead, we found superconductivity by growing few-layer stanene on PbTe/Bi2Te3/Si(111) substrate via molecular beam epitaxy [2][3]. The superconducting properties can be further modulated by varying the substrate thickness. Our experimental studies are further supported by first-principles calculations, which suggest that superconductivity occurs in a doped quantum spin Hall insulator. |
Tuesday, March 5, 2019 3:06PM - 3:18PM |
H05.00002: Growth and low temperature STM study of Stanene Jinfeng Jia Stanene and its derivatives can be 2D topological insulators (TI) with a very large band gap as proposed by first-principles calculations, or can support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall (QAH) effect. Here, we report a successful fabrication of 2D stanene by MBE. The atomic and electronic structures determined by STM and ARPES agree well with the predictions by first-principles calculations. Bulk band gap and edge states are also observed. On stanene thicker than 2 layers, superconductivity is also observed, which suggests stanene is a good candidate for topological superconductor. |
Tuesday, March 5, 2019 3:18PM - 3:30PM |
H05.00003: Tracking the motion of Josephson vortices and the Majorana fermion states bound to them in S-TI-S junctions networks designed for braiding Gilbert Arias, Erik Huemiller, Chad Germany, Guang Yue, Jessica H Montone, Dale J Van Harlingen
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Tuesday, March 5, 2019 3:30PM - 3:42PM |
H05.00004: Electron waiting times in hybrid junctions with topological superconductors Shuo Mi, Pablo Burset, Christian Flindt We investigate the waiting time distributions (WTDs) of superconducting hybrid junctions, considering both conventional and topologically nontrivial superconductors hosting Majorana bound states at their edges. To this end, we employ a scattering matrix formalism that allows us to evaluate the waiting times between the transmissions and reflections of electrons or holes. Specifically, we analyze normal-metal--superconductor (NIS) junctions and NISIN junctions, where Cooper pairs are spatially split into different leads. The distribution of waiting times is sensitive to the simultaneous reflection of electrons and holes, which is enhanced by the zero-energy state in topological superconductors. For the NISIN junctions, the WTDs of trivial superconductors feature a sharp dependence on the applied voltage, while for topological ones they are mostly independent of it. This particular voltage dependence is again connected to the presence of topological edge states, showing that WTDs are a promising tool for identifying topological superconductivity. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H05.00005: Study of Josephson trijunction constructed on Bi2Te3 surface Guang Yang, Zhaozheng Lyu, Junhua Wang, Jianghua Ying, Xiang Zhang, Guangtong Liu, Jie Fan, Zhongqing Ji, Xiunian Jing, Fanming Qu, Li Lu In 2008, Fu and Kane proposed that Josephson trijunctions constructed on the surface of topological insulators could host Majorana zero modes [1]. Such trijunctions could potentially serve as the basic components in a two-dimensional platform for realizing universal topological quantum computing [2]. In this talk, we will present the results of experimental investigations on trijunctions constructed on the surface of Bi2Te3. And we will compare the experimental results with Fu and Kane’s theory as well as with the results of numerical simulations based on a lattice model. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H05.00006: Observation of perfect Andreev reflection due to Klein paradox in a topological superconducting state in SmB6/YB6 heterostructures Seunghun Lee, Valentin Stanev, Xiaohang Zhang, Joshua S Higgins, Victor M Yakovenko, Johnpierre Paglione, Richard L. Greene, Victor Galitski, Ichiro Takeuchi Topological insulator, whose boundary states are described by the massless Dirac equation, is of great interest to realize unusual states of quantum matter. We report the observation of perfect Andreev reflection as a manifestation of Klein tunneling (perfect transmission of massless Dirac particles through any potential barrier) at the interface between a normal metal and a SmB6/YB6 heterostructure. We have previously demonstrated proximity-induced superconductivity in the surface state of SmB6. Conductance spectra of point contact junctions between a PtIr tip and the surface of the superconducting SmB6 show perfect conductance doubling within the induced superconducting gap (Δ). The absence of electron reflection under such finite Z is attributed to the interplay of the Dirac material in Andreev reflection process i.e., Klein tunneling. The observation can be described by a modified BTK theory with Dirac Hamiltonian, Dirac-BTK theory. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H05.00007: Meissner screening of Proximity coupled Topological Insulator/Superconductor Heterostructures Seokjin Bae, Seunghun Lee, Ichiro Takeuchi, Steven Anlage Meissner screening of proximity coupled SmB6/YB6 topological insulator-superconductor (TI/SC) thin-film-bilayers is studied through the temperature dependence of the effective penetration depth. A microwave resonator technique is used in which the bilayers are exposed to the rf magnetic field. The study is conducted by systematically varying the thickness of the SmB6 layer on top of the YB6 layer. Unconventional thickness dependence of the temperature profile of the effective magnetic penetration depth of the TI/SC bilayer is observed, which is distinctly different from that of the conventional metal/superconductor bilayers. This provides evidence for Meissner screening in the presence of bulk insulating states in the SmB6. Through an electromagnetic screening model, key parameters such as normal screening length, normal coherence length, thickness of the surface states, and Fermi velocity of SmB6 are extracted and found to be in reasonable agreement with previous studies. |
Tuesday, March 5, 2019 4:18PM - 4:30PM |
H05.00008: Experimental evidence of proximity induced odd-frequency superconductivity in a topological insulator Jonas Krieger, Sean Giblin, Thomas Prokscha, Andreas Suter, Thorsten Hesjedal, Zaher Salman At an interface between a topological insulator (TI) and a conventional superconductor, the topological surface states have been predicted to rearrange in an interesting fashion. The induced superconductivity between an s-wave superconductor and a TI surface state is expected to develop a complex p-wave order parameter which may allow to create a Majorana Fermions inside the core of a vortex. These collective excitations are their own antiparticles and are the basic element in a proposal for fault-tolerant quantum computing. Here we present experimental evidence for proximity induced superconductivity in a thin layer of the TI Bi2Se3 grown on top of Nb. From depth-resolved measurements in the Meissner state, we observe a local enhancement of the magnetic field in Bi2Se3 that exceeds the externally applied field, thus supporting the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state. |
Tuesday, March 5, 2019 4:30PM - 4:42PM |
H05.00009: How to systematically map out a Majorana island Jie Shen, Francesco Borsoi, Sebastian Heedt, Bernard Van Heck, Sasa Gazibegovic, Roy L. M. Op het Veld, John A Logan, Mihir Pendharkar, Marina Quintero Perez, Nick van Loo, Alexandra Fursina, Kevin Van Hoogdalem, Chris Palmstrom, Erik P. A. M. Bakkers, Leo Kouwenhoven As a high-quality hybrid system, InSb nanowires with epitaxial-grown Al shells reveal ballistic superconductivity and quantized zero-bias conductance peak. This holds great promise for the realization of Majorana-based topological quantum computing. The building block for a topological qubit is a superconductor-semiconductor island hosting a pair of Majorana zero modes (called Majorana island). The state of the topological qubit is the combination of the even/odd parity of such Majorana islands. Therefore, to understand the status of the topological qubit, systematic studies of a Majorana island are crucial. First, by performing tunnelling spectroscopy measurements, we use the ballistic superconductivity and quantized zero-bias peak to support the high-quality and potential ‘Majorana’ properties of the island. Secondly, the even-odd ground state phase diagram as a function of chemical potential is mapped out and provides a guideline for the topological qubit. Thirdly, how the superconducting gap and effective g-factor influence the phase diagram is also studied. Such a systematic mapping of the Majorana island is also suitable for double islands, leading towards topological qubits based on multiple islands. |
Tuesday, March 5, 2019 4:42PM - 4:54PM |
H05.00010: Realization of Majorana Zero Modes within a Topological Hinge State Berthold Jaeck, Yonglong Xie, Jian Li, Sangjun Jeon, Andrei B Bernevig, Ali Yazdani Higher order topological insulators (HOTI) host helical edge modes along its hinges that are protected by crystal and time-reversal symmetry. Proximity induced superconductivity on these hinge states is predicted to be topological in nature and provides a platform for the realization of Majorana zero modes (MZM). Theoretical modeling shows the emergence of MZMs in the hinge states at an interface where they are influenced by superconductivity and magnetism. Recently, bismuth was identified as a HOTI where scanning tunneling microscopy (STM) studies revealed the existence of hinge states on its surface (1). To realize this MZM platform, we grow bismuth thin films and iron clusters on a niobium surface. Using high-resolution spectroscopic mapping and spin-polarized STM, we characterize the influence of superconductivity and magnetism on the hinge states. Our measurements show the presence of localized zero energy states at the interface between superconducting hinge states and the iron clusters. Comparing various measurements with theoretical models, we will discuss how our observations are consistent with the presence of MZM. |
Tuesday, March 5, 2019 4:54PM - 5:06PM |
H05.00011: Radio frequency methods for Majorana based quantum computing: fast charge sensing and phase diagram mapping Davydas Razmadze, Deividas Sabonis, Filip Malinowski, Gerbold Menard, Sebastian Pauka, Hung Nguyen, David van Zanten, Eoin C O'Farrell, Judith Tabea Suter, Peter Krogstrup, Ferdinand Kuemmeth, Charles M Marcus We employ radio frequency techniques to demonstrate two measurements: first, by embedding an InAs/Al nanowire directly into a resonant circuit, it is possible to map key features of the conductance vs. gate-voltage phase diagram approximately 40 times faster than conventional lock-in methods; second, by capacitively coupling the same nanowire to a radio-frequency single electron transistor, fabricated from another nanowire, we demonstrate detection of single electron inter-island transitions, with signal-to-noise ratios exceeding 5 for an integration time below 1 μs at axial (parallel to nanowire) magnetic fields of 0.6T. Latter results will be the requirements for implementing Majorana based quantum computation in hybrid superconductor-semiconductor nanowire devices, and demonstrates the full compatibility of the high-bandwidth sensing techniques. Presented device geometries are similar to that have previously shown signatures of Majorana-like bound states. |
Tuesday, March 5, 2019 5:06PM - 5:18PM |
H05.00012: Advanced hybrid InSb/Al nanowires devices for topological parity readout (Part 1) Francesco Borsoi, Sebastian Heedt, Jie Shen, Senja Ramakers, Kun Zuo, Kevin Van Hoogdalem, Marina Quintero Perez, Sasa Gazibegovic, Roy L. M. Op het Veld, John A Logan, Mihir Pendharkar, Bernard Van Heck, Chris Palmstrom, Erik P. A. M. Bakkers, Leo P Kouwenhoven Majorana bound states (MBS) in hybrid semi-superconducting systems have been proposed to be the building blocks of the next quantum computers. Quantum information can be stored in the fermionic parity degree of freedom, shared in two well-separated MBS. A promising method to readout such parity is to measure the conductance through an Aharonov-Bohm (AB) interferometer, hosting a pair of MBS in one of the interfering arms. Here, we report our progress in the realization of such device based on InSb/Al islands. We first investigate the electron-phase evolution in a normal quantum dot embedded in an InSb nanowire network by mapping the phase of AB oscillations. Phase lapse and winding are extracted from the shift of these oscillations and from the associated Fano effect. Secondly, we study the energy spectrum of proximitized InSb nanowires in Coulomb blockade revealing gate-dependent ground state parity transitions as a function of magnetic field. Based on these results and on the development of a new nanofabrication technique, interferometric readout can be performed in both nano-networks and single-nanowire architectures. |
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