Pinning of Andreev bound states to zero energy in two-dimensional superconductor- semiconductor Rashba heterostructures

Majorana zero modes (MZMs) that obey the non-Abelian statistics have been intensively investigated for potential applications in topological quantum computing. The prevailing signals in tunneling experiments “fingerprinting” the existence of MZMs are the zero-energy bound states (ZEBSs). However, nearly all of the previously reported ZEBSs showing signatures of the MZMs are observed in difficult-to-fabricate heterostructures at very low temperatures and additionally require applied magnetic field. Here, by using in situ scanning tunneling spectroscopy, we detect the ZEBSs upon the interstitial Fe adatoms deposited on two different high-temperature superconducting one-unit-cell iron chalcogenides on SrTiO3(001). The spectroscopic results resemble the phenomenological characteristics of the MZMs inside the vortex cores of topological superconductors. Our experimental findings may extend the MZM explorations in connate topological superconductors toward an applicable temperature regime and down to the two-dimensional (2D) limit.

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Delocalisation of Majorana quasiparticles in plaquette–nanowire hybrid system

Scientific Reports ◽

10.1038/s41598-019-49227-5 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 6

Author(s):

Aksel Kobiałka ◽

Tadeusz Domański ◽

Andrzej Ptok

Keyword(s):

Bound States ◽

Spin Orbit Coupling ◽

Spin Orbit ◽

Two Dimensional ◽

Edge States ◽

Zero Energy ◽

One Dimensional ◽

Majorana Bound States ◽

Entire Structure ◽

Majorana Modes

Abstract Interplay between superconductivity, spin-orbit coupling and magnetic field can lead to realisation of the topologically non–trivial states which in finite one dimensional nanowires are manifested by emergence of a pair of zero-energy Majorana bound states. On the other hand, in two dimensional systems the chiral edge states can appear. We investigate novel properties of the bound states in a system of mixed dimensionality, composed of one-dimensional nanowire connected with two-dimensional plaquette. We study this system, assuming either its part or the entire structure to be in topologically non–trivial superconducting state. Our results show delocalisation of the Majorana modes, upon leaking from the nanowire to the plaquette with some tendency towards its corners.

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Zero-energy Andreev bound states from quantum dots in proximitized Rashba nanowires

Physical Review B ◽

10.1103/physrevb.98.245407 ◽

2018 ◽

Vol 98 (24) ◽

Cited By ~ 36

Author(s):

Christopher Reeg ◽

Olesia Dmytruk ◽

Denis Chevallier ◽

Daniel Loss ◽

Jelena Klinovaja

Keyword(s):

Quantum Dots ◽

Bound States ◽

Zero Energy ◽

Andreev Bound States

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EXCHANGE FIELD EFFECT ON THE ANDREEV BOUND STATE STUDIED BY FERROMAGNET/HIGH Tc SUPERCONDUCTOR INTERFACE

International Journal of Modern Physics B ◽

10.1142/s021797920502889x ◽

2005 ◽

Vol 19 (01n03) ◽

pp. 495-497 ◽

Cited By ~ 1

Author(s):

K.-W. NG ◽

MARIO FREAMAT

Keyword(s):

Bound States ◽

Bound State ◽

Exchange Field ◽

Zero Energy ◽

S Wave ◽

High Tc ◽

Andreev Bound States ◽

High Tc Superconductor ◽

Energy Peak ◽

Andreev Bound State

We have prepared Ag / BSCCO and Fe / Ag / BSCCO planar junctions to study the effect of Fe exchange field on the tunneling spectra. The junctions were constructed so that the tunneling direction is within the ab-plane, either along the maximum or minimum gap direction. Andreev bound states were observed as zero energy peak in the minimum gap direction. The exchange field caused major splitting of the zero energy peak, which did not occur in Ag / BSCCO junctions. We had detected a few percent (6 to 7%) of s-wave subcomponent at the interface in many of these junctions. This s-wave subcomponent had a Tc of about 20K.

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Large spatial extension of the zero-energy Yu–Shiba–Rusinov state in a magnetic field

Nature Communications ◽

10.1038/s41467-020-15322-9 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Zoltán Scherübl ◽

Gergő Fülöp ◽

Cătălin Paşcu Moca ◽

Jörg Gramich ◽

Andreas Baumgartner ◽

...

Keyword(s):

Magnetic Field ◽

Bound States ◽

Scanning Tunneling ◽

Zero Energy ◽

Tunneling Microscopy ◽

Numerical Renormalization Group ◽

Andreev Bound States ◽

Semiconductor Quantum Dot ◽

Spatial Extension ◽

The One

AbstractVarious promising qubit concepts have been put forward recently based on engineered superconductor subgap states like Andreev bound states, Majorana zero modes or the Yu-Shiba-Rusinov (Shiba) states. The coupling of these subgap states via a superconductor strongly depends on their spatial extension and is an essential next step for future quantum technologies. Here we investigate the spatial extension of a Shiba state in a semiconductor quantum dot coupled to a superconductor. With detailed transport measurements and numerical renormalization group calculations we find a remarkable more than 50 nm extension of the zero energy Shiba state, much larger than the one observed in very recent scanning tunneling microscopy measurements. Moreover, we demonstrate that its spatial extension increases substantially in a magnetic field.

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Reproducing topological properties with quasi-Majorana states

SciPost Physics ◽

10.21468/scipostphys.7.5.061 ◽

2019 ◽

Vol 7 (5) ◽

Cited By ~ 34

Author(s):

Adriaan Vuik ◽

Bas Nijholt ◽

Anton Akhmerov ◽

Michael Wimmer

Keyword(s):

Bound States ◽

Josephson Effect ◽

Tunnel Barrier ◽

Topological Properties ◽

Zero Energy ◽

Tunneling Spectrum ◽

Zero Bias ◽

Andreev Bound States ◽

Zero Bias Conductance ◽

Coupling Strengths

Andreev bound states in hybrid superconductor-semiconductor devices can have near-zero energy in the topologically trivial regime as long as the confinement potential is sufficiently smooth. These quasi-Majorana states show zero-bias conductance features in a topologically trivial phase, mimicking spatially separated topological Majorana states. We show that in addition to the suppressed coupling between the quasi-Majorana states, also the coupling of these states across a tunnel barrier to the outside is exponentially different for increasing magnetic field. As a consequence, quasi-Majorana states mimic most of the proposed Majorana signatures: quantized zero-bias peaks, the 4\pi4π Josephson effect, and the tunneling spectrum in presence of a normal quantum dot. We identify a quantized conductance dip instead of a peak in the open regime as a distinguishing feature of true Majorana states in addition to having a bulk topological transition. Because braiding schemes rely only on the ability to couple to individual Majorana states, the exponential control over coupling strengths allows to also use quasi-Majorana states for braiding. Therefore, while the appearance of quasi-Majorana states complicates the observation of topological Majorana states, it opens an alternative route towards braiding of non-Abelian anyons and protected quantum computation.

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What can Andreev bound states tell us about superconductors?

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2014.0143 ◽

2018 ◽

Vol 376 (2125) ◽

pp. 20140143 ◽

Cited By ~ 1

Author(s):

Oded Millo ◽

Gad Koren

Keyword(s):

Order Parameter ◽

Bound States ◽

Domain Walls ◽

High Temperature Superconductors ◽

Zero Energy ◽

Zero Bias ◽

Andreev Bound States ◽

Triplet Pairing ◽

Phase Ordering ◽

Crossed Andreev Reflection

Zero-energy Andreev bound states, which manifest themselves in the tunnelling spectra as zero-bias conductance peaks (ZBCPs), are abundant at interfaces between superconductors and other materials and on the nodal surface of high-temperature superconductors. In this review, we focus on the information such excitations can provide on the properties of superconductor systems. First, a general introduction to the physics of Andreev bound states in superconductor/normal metal interfaces is given with a particular emphasis on why they appear at zero energy in d -wave superconductors. Then, specific spectroscopic tunnelling studies of thin films, bilayers and junctions are described, focusing on the corresponding ZBCP features. Scanning tunnelling spectroscopy (STS) studies show that the ZBCPs on the c -axis YBa 2 Cu 3 O 7− δ (YBCO) films are correlated with the surface morphology and appear only in proximity to (110) facets. STS on c -axis La 1.88 Sr 0.12 CuO 4 (LSCO) films exhibiting the 1/8 anomaly shows spatially modulated peaks near zero bias associated with the anti-phase ordering of the d -wave order parameter predicted at this doping level. ZBCPs were also found in micrometre-size edge junctions of YBCO/SrRuO 3 /YBCO, where SrRuO 3 is ferromagnetic. Here, the results are consistent with a crossed Andreev reflection effect (CARE) at the narrow domain walls of the SrRuO 3 . ZBCPs measured in STS studies of manganite/cuprate bilayers could not be attributed to CARE because the manganite's domain wall is much larger than the coherence length in YBCO, and instead are attributed to proximity-induced triplet-pairing superconductivity with non-conventional symmetry. And finally, ZBCPs found in junctions of non-intentionally doped topological insulator films of Bi 2 Se 3 and the s -wave superconductor NbN are attributed to proximity-induced p x + i p y triplet order parameter in the topological material. This article is part of the theme issue ’Andreev bound states’.

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