scholarly journals Conductance asymmetries in mesoscopic superconducting devices due to finite bias

2021 ◽  
Vol 10 (2) ◽  
Author(s):  
André Melo ◽  
Chun-Xiao Liu ◽  
Piotr Rożek ◽  
Tómas Örn Rosdahl ◽  
Michael Wimmer
Keyword(s):  
Bound States ◽  
Voltage Dependence ◽  
Superconducting Devices ◽  
Scattering Matrix ◽  
Tunnel Barrier ◽  
Tunneling Conductance ◽  
Physical Origin ◽  
Andreev Bound States ◽  
Superconducting Device ◽  
Symmetry Relations

Tunneling conductance spectroscopy in normal metal-superconductor junctions is an important tool for probing Andreev bound states in mesoscopic superconducting devices, such as Majorana nanowires. In an ideal superconducting device, the subgap conductance obeys specific symmetry relations, due to particle-hole symmetry and unitarity of the scattering matrix. However, experimental data often exhibits deviations from these symmetries or even their explicit breakdown. In this work, we identify a mechanism that leads to conductance asymmetries without quasiparticle poisoning. In particular, we investigate the effects of finite bias and include the voltage dependence in the tunnel barrier transparency, finding significant conductance asymmetries for realistic device parameters. It is important to identify the physical origin of conductance asymmetries: in contrast to other possible mechanisms such as quasiparticle poisoning, finite-bias effects are not detrimental to the performance of a topological qubit. To that end we identify features that can be used to experimentally determine whether finite-bias effects are the source of conductance asymmetries.

scholarly journals Order, disorder, and tunable gaps in the spectrum of Andreev bound states in a multiterminal superconducting device

2017 ◽  
Vol 95 (4) ◽  
Author(s):  
Tomohiro Yokoyama ◽  
Johannes Reutlinger ◽  
Wolfgang Belzig ◽  
Yuli V. Nazarov
Keyword(s):  
Bound States ◽  
Andreev Bound States ◽  
Superconducting Device

Suppressed Andreev reflection and helical Andreev bound states in triplet superconductor three-dimensional topological insulator

2015 ◽  
Vol 29 (04) ◽  
pp. 1550018 ◽  
Author(s):  
M. Khezerlou ◽  
H. Goudarzi
Keyword(s):  
Topological Insulator ◽  
Bound States ◽  
Andreev Reflection ◽  
Chemical Potential ◽  
Three Dimensional ◽  
P Wave ◽  
Superconducting Gap ◽  
Tunneling Conductance ◽  
Andreev Bound States ◽  
Josephson Supercurrent

Effect of proximity-induced unconventional p-wave superconductivity in a three-dimensional topological insulator-based S/F/S structure on the Andreev bound states (ABSs) and Josephson supercurrent is studied. We investigate, in detail, the suppression of Andreev reflection and helical ABSs in the presence of three types of triplet superconducting gap. The magnetization of ferromagnetic section is perpendicular to the surface of junction. The influence of such features on the supercurrent flow on the surface of the topological insulator is studied. We carry out our goal by introducing a relevant form of Dirac spinors for gapless renormalized by chemical potential μ excitation states. Therefore, it enables us to consider the virtual Andreev process, simultaneously, and we propose to investigate it in a tunneling conductance junction. It is shown that the results obtained in this case are completely different from those in conventional superconductivity, as s- or d-waves, for example, the magnetization is found to decrease the gap for px and px+ipy case, whereas increase it for py order. Strongly suppressed Andreev reflection is demonstrated.

scholarly journals Reproducing topological properties with quasi-Majorana states

2019 ◽  
Vol 7 (5) ◽  
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.

scholarly journals Nonlocal Conductance Spectroscopy of Andreev Bound States: Symmetry Relations and BCS Charges

2020 ◽  
Vol 124 (3) ◽  
Author(s):  
Jeroen Danon ◽  
Anna Birk Hellenes ◽  
Esben Bork Hansen ◽  
Lucas Casparis ◽  
Andrew P. Higginbotham ◽  
...  
Keyword(s):  
Bound States ◽  
Andreev Bound States ◽  
Symmetry Relations

scholarly journals Andreev bound states in ferromagnet-superconductor nanostructures

2003 ◽  
Vol 387 (1-2) ◽  
pp. 7-12 ◽  
Author(s):  
M. Krawiec ◽  
B.L. Györffy ◽  
J.F. Annett
Keyword(s):  
Bound States ◽  
Andreev Bound States

scholarly journals Flow of S-matrix poles for elementary quantum potentials1This research was supported in part by an NSERC Undergraduate Summer Research Award (SGN) and an NSERC Discovery Grant (MAW).

2011 ◽  
Vol 89 (11) ◽  
pp. 1127-1140 ◽  
Author(s):  
B. Belchev ◽  
S.G. Neale ◽  
M.A. Walton
Keyword(s):  
Bound States ◽  
Scattering Matrix ◽  
Nucl Phys ◽  
Quantum Scattering ◽  
Research Award ◽  
Momentum Plane ◽  
S Matrix ◽  
Potential Depth ◽  
Square Well ◽  
Insight Into

The poles of the quantum scattering matrix (S-matrix) in the complex momentum plane have been studied extensively. Bound states give rise to S-matrix poles, and other poles correspond to non-normalizable antibound, resonance, and antiresonance states. They describe important physics but their locations can be difficult to determine. In pioneering work, Nussenzveig (Nucl. Phys. 11, 499 (1959)) performed the analysis for a square well (wall), and plotted the flow of the poles as the potential depth (height) varied. More than fifty years later, however, little has been done in the way of direct generalization of those results. We point out that today we can find such poles easily and efficiently using numerical techniques and widely available software. We study the poles of the scattering matrix for the simplest piecewise flat potentials, with one and two adjacent (nonzero) pieces. For the finite well (wall) the flow of the poles as a function of the depth (height) recovers the results of Nussenzveig. We then analyze the flow for a potential with two independent parts that can be attractive or repulsive, the two-piece potential. These examples provide some insight into the complicated behavior of the resonance, antiresonance, and antibound poles.

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