Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S05: Topological Superconductivity: NanowiresFocus
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Anushya Chandran, Boston University Room: BCEC 108 |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S05.00001: Surface superconductivity in gold – a material platform for Majorana bound states Invited Speaker: Peng Wei Proximity effect in multilayer heterostructures allows the creation of new quasiparticles with mixed physical characters. In particular, it may lead to the emergence of Majorana bound states (MBS) by mixing superconductivity, ferromagnetism, and spin-orbit coupling at material interfaces. Inducing superconductivity and magnetic exchange interactions in well-defined Shockley surface states (SS) of high quality ultrathin Au(111) layers has been predicted as an excellent platform for MBS [1]. In this talk, I will first present our device based heterostructure platform for creating and investigating such hybrid superconducting states in Au(111) [2]. By means of electron tunneling spectroscopy, I will demonstrate signatures of superconductivity induced in the two-dimensional SS of Au(111) thin film, as well as the behavior of such superconducting state under a planar Zeeman field. Unlike conventional proximity effects, the induced superconductivity in SS that are physically separated from a bulk superconductor may be governed by indirect quasiparticle scattering processes, which would further allow the manipulations of SS for MBS. Our results on planar tunneling devices made of scalable nanowires fabricated from such Au(111) heterostructures will be discussed. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S05.00002: Backbones of a Topological Qubit – High Quality Selective-Area Grown InSb Nanowire Networks using MBE Guanzhong Wang, Pavel Aseev, Luca Binci, Amrita Singh, Lieuwe Stek, Frenk Boekhout, Senja Ramakers, Jie Shen, John Watson, Leo P Kouwenhoven, Gijs De Lange, Philippe Caroff Nanowires (NW) made from III-V semiconductors are arguably the most mature platform for studying topological superconductivity and realizing Majorana bound states. So far progress on this front has been restricted to single NWs grown with conventional vapor-liquid-solid method. Although this growth mechanism is capable of producing free-standing NW crosses and hashtags, realization of more complex networks calls for an in-plane strategy to achieve new lithographically defined structures. Here, we implement such in-plane synthesis of InSb NW networks by selective area growth (SAG) using molecular-beam epitaxy (MBE). We perform structural and transport characterization to assess the crystal quality and electronic properties. The high quality of electron transport in InSb NWs and crosses are verified by both classical mobility and quantum transport measurements, with Hall mobility reaching 17,000 cm2/(V*s) and well-defined quantum point contact conductance plateaus at finite magnetic field. We also demonstrate phase coherent transport by studying Aharonov-Bohm interference in loops and induced superconductivity in an Al-covered sample. These results combined make InSb SAG a promising material platform for realizing a topological qubit. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S05.00003: Demonstration of Majorana Fermion Pairs in Superconducting gold Surface States Sujit Manna, Peng Wei, Yingming Xie, Kam Tuen Law, Patrick Lee, Jagadeesh Moodera We present strong evidence for the emergence of Majorana bound states (MBS) in gold nanowires with proximitized superconductivity, as theoretically predicted.1 The interplay between superconductivity, spin-orbit coupling (SOC) and Zeeman field laid the foundation to realize MBS. We have experimentally achieved novel heterostructures, achieving these three interactions, and developed a unique method to fabricate such heterostructures into scalable nanowires. Using high-resolution scanning tunneling microscopy (STM) under in-plane magnetic field, we show that MBS appears in pairs at the opposite edges of a magnetic nanostructure on Au nanowire at 350 mK. Such spatially resolved pair of bound states, confirmed by further theoretical modeling, provides strong support for the observation of MBS in Au nanowire systems. It opens up the possibility for realizing MBS manipulations in stable and scalable metallic thin-film nanostructures, where strong SOC ensures much more robust MBS compared to other analogous semiconductor-based schemes. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S05.00004: From Spintronics to Majorana Bound States Igor Zutic, Tong Zhou, Narayan Mohanta, Jong E Han, Alex Matos Abiague Magnetic textures, widely used to store information, can also provide synthetic spin-orbit coupling and confinement, supporting the creation of topologically nontrivial states, such as skyrmions and Majorana bound states (MBS) [1,2]. By a careful design of an array of magnetic nanopillars (MNPs), based on finite-element simulations, the resulting magnetic textures modify a proximity-induced superconductivity in the nearby 2D electron gas to form effective topological wires with MBS emerging at their ends [3]. Using spin-transfer torque, common to spintronics, to control magnetic textures [4], these topological wires can be reconfigured to implement fusion and braiding of MBS [2]. We show that a generalized topological condition for MBS formation [2] can also guide the understanding of the MBS evolution in realistic MNP arrays [3]. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S05.00005: Interacting Shiba States on Proximitized Superconducting Surface of Bi Yuwen Hu, Hao Ding, Mallika Randeria, Ali Yazdani Magnetic atoms on the surface of a superconductor induce in-gap Shiba states that can be hybridized to create a topological superconducting phase when placed in one-dimensional chains, with Majorana zero modes localized at their ends [1,2]. We have performed measurements of magnetic adatoms deposited on the surface of epitaxially grown Bi(110) thin films on a superconducting Nb(110) surface using a dilution refrigerator scanning tunneling microscope (STM). Our spectroscopic measurements show the Bi surface to exhibit a hard superconducting gap of 1.6 meV and the presence of Shiba states near magnetic adatoms. Using atomic manipulation techniques with the STM, we have built dimers of magnetic atoms with varying distance and geometry and detected the hybridization of individual in-gap states into “Shiba molecules”. We will report on these results and our efforts to build chains of magnetic atoms on the surface of superconducting Bi. The strong spin-orbit coupling and the large induced superconducting gap by the Nb substrate make this Bi surface an attractive platform for creation of atomic chains that host Majorana zero modes. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S05.00006: De-localized states in three-terminal InSb nanowire devices Peng Yu, Jun Chen, Moira Hocevar, Ghada Badawy, Sasa Gazibegovic, Roy Op het Veld, Sébastien Plissard, Erik P. A. M. Bakkers, Sergey M Frolov Majorana bound states(MBS) has been predicted to emerge in 1D nanowire with induced superconductivity, spin-orbital coupling and external magnetic field. Although zero bias peak(ZBP) has been observed in different systems for years, no tunneling spectroscopy has verified the existence of the two Majorana bound states that should appear at the boundaries of the topological regime. We fabricated three-terminal devices with 400nm long superconducting contact in the middle and de-localized states have been observed from two sides measured simultaneously. On the contrary of the regime where the ZBP usually be observed in two terminal devices, those de-localized states appear in more open regime with more subbands available. Ongoing measurements will be dedicated to answer whether ZBP could appear in that regime and be observed from two sides. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S05.00007: Flux-induced Majorana modes in full-shell nanowires Saulius Vaitiekenas, Mingtang Deng, Peter Krogstrup, Charles M Marcus We demonstrate a novel means of creating Majorana zero modes using magnetic flux applied to a full superconducting shell surrounding a semiconducting nanowire core, unifying approaches based on proximitized nanowires and vortices in topological superconductors. In the destructive Little-Parks regime, reentrant regions of superconductivity are associated with an integer number of phase windings in the shell. Tunneling into the core reveals a hard induced gap near zero applied flux, corresponding to zero phase winding, and a gapped region with a discrete zero-energy state for flux around $\Phi_{0} = h/2e$, corresponding to $2 \pi$ phase winding. Coulomb peak spacing in full-shell islands around one applied flux shows exponentially decreasing deviation from $1e$ periodicity with device length, consistent with the picture of Majorana modes located at the ends of the wire. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S05.00008: Advanced hybrid InSb/Al nanowires devices for topological parity readout (Part 2) Sebastian Heedt, Marina Quintero Perez, Francesco Borsoi, Alexandra Fursina, Nick van Loo, Jie Shen, Chien-An Wang, Kevin Van Hoogdalem, Badawy Ghada, Sasa Gazibegovic, Erik P. A. M. Bakkers, Leo P Kouwenhoven Majorana bound states (MBS) are expected to enable topological qubits that encode quantum information with particularly long coherence times. The qubit state is stored non-locally in the fermion parity of multiple pairs of MBS hosted on a semiconducting-superconducting charge island. Interferometric readout of these qubits requires phase-coherent loops that comprise high-mobility InSb nanowires and Al to enable proximity-induced superconductivity in the semiconductor. Here, we introduce a fundamentally new approach for the realization of these hybrid devices based on a novel technique for the selective deposition of the Al thin films. We combine this technique with atomic hydrogen cleaning of the nanowires to remove native oxide prior to the Al deposition. The induced superconductivity in the nanowires is demonstrated via voltage-bias spectroscopy and by probing the critical currents in InSb Josephson junctions. Moreover, Cooper pair tunneling is studied in mesoscopic InSb/Al islands and parity transitions are investigated as a function of the applied magnetic field. Finally, advanced circuits are introduced that allow to study basic elements of the prospective topological qubit. |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S05.00009: Quantum-Transport in Semiconductor Nanowire Josephson Junctions Praveen Sriram, Sandesh S Kalantre, Kaveh Gharavi, Jonathan D Baugh, Bhaskaran Muralidharan Semiconductor nanowire-superconductor hybrid systems provide a promising platform for hosting unpaired Majorana fermions and thus realizing fault-tolerant topological qubits. In this study, we employ the Non-Equilibrium Green’s Function (NEGF) Formalism to model quantum transport in normal (N)-superconductor(S) junctions. We analyze Josephson junctions based on semiconductor nanowires and derive the Andreev bound state spectrum and current-phase relations. Recently, [1], and [2] have reported oscillations in the critical supercurrent with an axial magnetic field. Our simulations indicate that this phenomenon arises from the interference of orbital angular momentum modes of the cylindrical nanowire. We add disorder and study its effect on the critical current oscillations, with an aim to gain a thoroughgoing understanding of the experiments. |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S05.00010: Hysteresis from Nonlinear Dynamics of Majorana Zero Modes in Topological Josephson Junctions Jia-Jin Feng, Zhao Huang, Zhi Wang, Qian Niu We reveal that topological Josephson junctions provide a natural platform for the interplay between the Josephson effect and the Landau-Zener effect through a two-level system formed by coupled Majorana modes. We build a quantum resistively shunted (RSJ) junction model by modifying the standard textbook RSJ model to take account of the two-level system from the Majorana modes at the junction. We show that the dynamics of the two-level system is governed by a nonlinear Schroedinger equation and solve the equations analytically via a mapping to a classical dynamical problem. This nonlinear dynamics leads to hysteresis in the I-V characteristics, which can give a quantitative explanation to recent experiments. We also predict coexistence of two interference patterns with periods h/e and h/2e in topological superconducting quantum interference devices. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S05.00011: Current-Controlled Majorana Bound States in Hybrid Semiconductor-Superconductor Nanowires Deposited on Magnetic Stripe Domains Narayan Mohanta, Tong Zhou, Jong E Han, Andrew D Kent, Javad Shabani, Igor Zutic, Alex Matos Abiague The fringing fields created by magnetic stripes formed in magnetic films [1] generate inhomogeneous magnetic textures on length scales as large as 2 microns. A hybrid semiconductor-superconductor nanowire deposited on the top of a magnetic film in the stripe phase experiences a large synthetic spin-orbit coupling resulting from the fringing fields [2] of the striped domains. We show that such a system can support the formation of Majorana bound states (MBS) localized at the ends of the wire. We investigate the transition to the topological superconducting phase as a function of the stripes size and orientation, which can be tuned by applying a charge current through the magnetic film. This produces changes in the fringing magnetic texture acting on the nanowire and eventually leads to a topological phase transition with the corresponding emergence or destruction of MBS [2]. The proposed platform is promising for electrically tuning MBS in a non-invasive way and without the need for external magnetic fields. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S05.00012: Quantized zero bias conductance plateaus in hybrid nanowire topological quantum information processing platforms without non-Abelian Majorana zero modes Christopher Moore, Chuanchang Zeng, Tudor Dan Stanescu, Sumanta Tewari Braiding operations in topological quantum computations inherently rely on the spatial separation between Majorana bound states (MBSs), as a result a method of distinguishing between these quasi-Majorana states and true Majorana zero modes (MZMs), localized at the ends of a semiconductor-superconductor (SM-SC) nanowire, is essential in the creation of a topological quantum bit. Here we show that recently observed, 2e^2/h-quantized zero-bias conductance plateaus, may arise in SM-SC nanowires due to the presence of quasi-Majorana states, for which the constituent MBSs are specially separated on the order of the Majorana decay length. Because these quasi-Majoranas form rather generically within the topologically trivial regime, our results establish that the observation of 2e^2/h-quantized zero-bias conductance plateaus does not represent sufficient evidence of the existence of non-Abelian MZMs localized at the opposite ends of a wire. Thus, we conclude that localized charge tunneling measurements, so far considered the primary probe for the existence of MZMs, have exhausted their potential to reveal useful information in distinguishing MZMs from low energy Andreev bound states within SM-SC hybrid structures. |
Thursday, March 7, 2019 2:03PM - 2:15PM |
S05.00013: Onset of the 4π-periodic Josephson effect and dissipative response at the Majorana phase transition in a semiconducting nanowire junction Chaitanya Murthy, Bernard Van Heck, Leonid Glazman, Chetan Nayak We study the appearance of the 4π-periodicity of the Josephson energy in a single-channel semiconducting nanowire junction much shorter than the coherence length. We compute analytically the Josephson energy of the junction as a function of magnetic field, taking into account the contributions of both discrete and continuous spectrum. We show that, in the limit of perfect transmission, the spectrum of the junction is gapless for a finite range of phase difference and a finite range of magnetic fields on the topological side of the transition. We also study the finite-frequency admittance of the junction, paying particular attention to the critical regime. We show that the expected critical behavior near the phase transition only appears in the current-current correlation function at sub-leading order in the ratio of the induced superconducting gap to the spin-orbit energy, a fact that can be understood within the critical theory of a helical, neutral Majorana mode. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700