Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G42: Topological Superconductivity in Nanowires and One-dimensional SystemsFocus
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Sponsoring Units: DMP Chair: Mitra Sedeeqi, Binghamton University Room: Room 318 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G42.00001: Phase Diagram of InAs-Al Heterostructures Invited Speaker: Lucas Casparis Superconductor-semiconductor hybrid nanowires have been predicted to host a topological phase in the bulk and Majorana zero modes at the ends of the wire. Probing the full extent of this prediction has been challenging since the traditional two-terminal device geometries are limited to probe the local density of states at one end of the wire. In this context, we recently developed three-terminal devices which allow for the measurement of the transport gap in the bulk of the wire, as well as the detection of correlated local states at both ends of the wire. |
Tuesday, March 7, 2023 12:06PM - 12:18PM Author not Attending |
G42.00002: Charge tunneling events within hybridized triple quantum dots Lin Han, Michael Chan, Christian G Prosko, Damaz De Jong, Yu Liu, Leo P Kouwenhoven, Filip K Malinowski Towards the realization of topological quantum computation, dispersive gate sensing plays an important role for qubit readout, which enables characterization and further measurements of a quantum system in floating regime. In our work, we define a superconducting island in between two semiconducting quantum dots on an InAs nanowire. We investigate electron cotunneling between the quantum dots through the superconducting island, and observe cross Andreev reflections for several settings of the barrier gates. With multiplexing, we notice that the resonator signal from the middle island is less sensitive to the cotunneling events, while that from the outer dots is affected by all charge transitions. By analyzing the capacitance of various charge transitions, we explore the tunneling properties of the hybrid system. Our result will assist in the tuning of many-sites Kitaev chains and scalable topological qubits in the future. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G42.00003: Disconnected entanglement entropy and fermion parity noise for the conclusive electrical detection of Majorana zero modes Arnav Arora, Abhishek Kejriwal Rashba nanowire-superconductor hybrids are under intense scrutiny with respect to the conclusive sighting of Majorana zero modes (MZM). Protocols for their conclusive detection based on local and non-local conductance signatures have been subject to intense scrutiny and altercations [1]. We extend the idea of topological entanglement entropy [2,3] to faithfully distinguish between true MZMs and trivial Quasi-MZMs in a Rashba nanowire setup. We demonstrate that the disconnected entanglement entropy, derived from the von Neumann entanglement entropy, provides a distinct and robust signature of the topological phase transition which is immune to system parameters, size and disorders. In order to understand the entanglement entropy of the Rashba nanowire system, we establish its connection to a model of interacting spinfull Kitaev chains. Moreover, we relate the entanglement entropy to a physical observable of the system — the fermion parity noise [4], and show that it behaves concordantly with entanglement entropy, hence nominating it as a suitable metric for the detection of MZMs. We comment on possible transport signatures beyond the conductance spectra for possibly connecting this construct to actual measurements. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G42.00004: Crossed Andreev reflection and elastic co-tunneling optimization using magnetic field Alberto Bordin, Guanzhong Wang, Chun-Xiao Liu, Sebastiaan ten Haaf, Grzegorz P Mazur, Nick van Loo, Di Xu, David van Driel, Francesco Zatelli, Ghada Badawy, Sasa Gazibegovic, Erik P. A. M. Bakkers, Michael Wimmer, Leo P Kouwenhoven, Tom Dvir A short superconducting segment can mediate two peculiar interactions between attached quantum dots: elastic co-tunneling (ECT) and crossed Andreev reflection (CAR). Such interacting quantum dots can realize a minimal Kitaev chain hosting Majorana bound states, provided that the interaction is strong and the ratio between the two processes can be controlled. In our device, CAR and ECT are mediated by Andreev bound states formed in a hybrid semiconductor-superconductor heterostructure. We show that the combination of the intrinsic InSb nanowire spin-orbit coupling and an applied magnetic field provides an efficient knob to tune the ratio between CAR and ECT as well as their strength. By rotating the magnetic field, we show how to deterministically reach a ratio equal to 1, the so-called poor man's Majorana sweet-spot. If the field is rotated in 3D, then the sweet-spot becomes a manifold, in which we can locate a sweetest-spot: the point where CAR equals ECT and their value is maximal. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G42.00005: Probing weak antilocalization in gate-defined semiconductor wires Seyed Mohammad Farzaneh, Neda Lotfizadeh, William F Schiela, PENG YU, Ido Levy, Javad Shabani Weak localization and weak antilocalization are macroscopic signatures of quantum interference in a low dimensional electron system. Quasi-one-dimensional semiconductor wires with large spin-orbit coupling are considered as a platform for exploring topological phases of matter and realizing majorana zero modes. Gate-defined wires grown using molecular beam epitaxy are expected to be less disordered than nanofabricated 1D structures or self-assembled nanowires. They also provide better control over carrier density. We study the spin-orbital properties of electrons in gate-defined InAs wires by comparing wires with different widths and orientations with respect to the crystal axes. In the presence of an in-plane magnetic field, one can extract information about spin-orbit coupling and spin texture by measuring the magnetoconductivity. The results are generalizable to all semiconductors with a zinc blende structure and are useful in different applications from spintronics to the physical realization of topological quantum computation. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G42.00006: Superconducting diode effect due to magnetochiral anisotropy in topological insulator and Rashba nanowires Jelena Klinovaja The critical current of a superconductor can depend on the direction of current flow due to magnetochiral anisotropy when both inversion and time-reversal symmetry are broken, an effect known as the superconducting (SC) diode effect. Here, we consider one-dimensional (1D) systems in which superconductivity is induced via the proximity effect. In both topological insulator and Rashba nanowires, the SC diode effect due to a magnetic field applied along the spin-polarization axis and perpendicular to the nanowire provides a measure of inversion symmetry breaking in the presence of a superconductor. Furthermore, a strong dependence of the SC diode effect on an additional component of magnetic field applied parallel to the nanowire as well as on the position of the chemical potential can be used to detect that a device is in the region of parameter space where the phase transition to topological superconductivity is expected to arise. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G42.00007: Planar tunneling along EuS nanowire edge junctions formed over Au(111) for topological superconductivity Jason Tran, Yasen Hou, En-De Chu, Patrick A Lee, Jagadeesh S Moodera, Peng Wei Metallic surface states, such as those in Au(111), with strong Rashba spin-orbit coupling and induced superconductivity could host topological superconductivity when coupled to the nanostructures of magnetic insulators, for example EuS [1,2]. Following our prior work [1], we report our progress on fabricating scalable EuS nanowires coupled to Au(111) surface. We further fabricate planar tunneling devices with highly transparent junctions at the ends of the EuS nanowires and carry out local tunneling spectroscopy down to milli-Kelvin temperatures. The transparent junctions allow us to resolve the sub-gap states with finer energy resolution, and the evolution of the sub-gap states under an applied planar magnetic field. We will discuss our studies on the sub-gap states including the zero bias conductance peak, in particular those features that are limited by thermal broadening. We will further discuss the connections between our results and topological superconductivity. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G42.00008: Zero energy modes of artificial spin chains from first-principles calculations Balazs Ujfalussy, Bendegúz Nyári, Laszlo Szunyogh, Andras Laszloffy The conditions under which Majorana zero modes (MZM) appear and what are their physical properties in realistic materials have been of high interest over the past few years triggered by their possible applications as fault-tolerant quantum bits. The MZMs are topological states corresponding to triplet pairing at zero energy emerging in an inner gap inside the superconducting gap. However, experimentally it is very challenging to uniquely identify MZMs based solely on their spectral properties. Fully relativistic first-principles calculations based on the solution of the Bogoliubov-de Gennes equations are able to reproduce the measured spectral quantities and provide additional information on the nature of the in-gap states reported in corresponding experiments. In this work we present calculations in the superconducting state of the in-gap density of states, the singlet and triplet order parameters and various related quantities for Fe and Mn chains on pure Ta(110) and Au monolayer covered Nb(110) surface. The chains of magnetic ad-atoms are also assumed to be in various artificial spin-spiral states. In a wide range of the spin-spiral wavelength, we find an inner gap with states at zero energy and a large triplet pairing order parameter. Our results are then compared to experiments where possible and discuss the formation of MZMs in a material-specific way |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G42.00009: A Minimal Nanowire-Based Kitaev Chain Using Proximitised Quantum Dots (Part 1) David van Driel, Guanzhong Wang, Di Xu, Tom Dvir, Alberto Bordin, Bart Roovers, Francesco Zatelli, Greg Mazur, Nick van Loo, Sasa Gazibegovic, Ghada Badawy, Erik P. A. M. Bakkers, Leo P Kouwenhoven Majorana bound states are highly sought-after quasi-particles, mainly due to their non-abelian statistics. This property is desirable both for fundamental research and possible applications in the field of quantum computing. The Kitaev model predicts that Majorana bound states appear at the ends of quantum dot-superconductor chains [1]. A two-site version of such a chain was reported recently [2]. Here, non-topological Majorana bound states appear when the system is tuned to a sweet spot. These Poor Man's Majoranas manifest themselves as zero bias conductance peaks and exhibit stability against local perturbations of the Majorana bound states, i.e. varying quantum dot energies in the chain [3]. Therefore, a finite energy splitting is expected when the system moves away from the sweet spot. Introducing a superconducting pairing in the quantum dots can increase reproducibility and stability of this sweet spot. We study Poor Man's Majoranas for different superconducting pairing versus charging energy ratios of the two quantum dots. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G42.00010: Building a minimal Kitaev chain using proximitized quantum dots at the charge-neutral sweet spot Guanzhong Wang, David van Driel, Di Xu, Francesco Zatelli, Tom Dvir, Alberto Bordin, Greg Mazur, Nick van Loo, Bart Roovers, Sasa Gazibegovic, Ghada Badawy, Erik P. A. M. Bakkers, Leo P Kouwenhoven
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Tuesday, March 7, 2023 1:54PM - 2:06PM |
G42.00011: Circuit QED signatures of Majorana bound states in semiconductor nanowires with spin-orbit-induced subband mixing Chi Zhang, Ryan Tiew, Kristof Moors, Malcolm R Connolly Circuit quantum electrodynamics (cQED) is a powerful toolset enabling the study of interaction between light and microscopic degrees of freedom in superconducting circuits. Recently, this toolset enabled resolving the spectrum of Andreev bound states (ABSs) in Josephson junctions based on III-V materials with strong spin-orbit coupling through their microwave transitions. Here, we consider such transitions in the topological regime with large external magnetic field, where more exotic Majorana bound states (MBSs) are predicted to appear. With detailed tight-binding simulations, we resolve the Andreev spectrum and examine how the cQED signatures of ABSs evolve from the known zero-field limit into the topological regime. We go beyond the conventional Lutchyn-Oreg model and consider multiple transverse modes and their spin-orbit-induced mixing. In this way, we find that MBSs originating from the lowest transverse mode mix with ABSs from higher modes deep in the topological regime. The subband mixing turns on microwave transitions involving MBSs, which would otherwise remain invisible. Our results point towards the possibility of direct cQED characterization of MBSs in a topological Josephson junction. |
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