scholarly journals Andreev bound states and their signatures

2018 ◽  
Vol 376 (2125) ◽  
pp. 20180140 ◽  
Author(s):  
J. A. Sauls
Keyword(s):  
State Formation ◽  
Quantum Coherence ◽  
Bound States ◽  
Andreev Reflection ◽  
Bound State ◽  
Unconventional Superconductivity ◽  
Excitation Energies ◽  
Andreev Bound States ◽  
Properties Of Superconductors ◽  
Andreev Scattering

Many of the properties of superconductors related to quantum coherence are revealed when the superconducting state is forced to vary in space in response to an external magnetic field, a proximity contact, an interface to a ferromagnet or to impurities embedded in the superconductor. Among the earliest examples is Andreev reflection of an electron into a retro-reflected hole at a normal-superconducting interface. In regions of strong inhomogeneity, multiple Andreev reflection leads to the formation of sub-gap states, Andreev bound states , with excitation energies below the superconducting gap. These states play a central role in our understanding of inhomogeneous superconductors. The discoveries of unconventional superconductivity in many classes of materials, advances in fabrication of superconducting/ferromagnetic hybrids and nanostructures for confining superfluid 3 He, combined with theoretical developments in topological quantum matter have dramatically expanded the significance of branch conversion scattering and Andreev bound state formation. This collection of articles highlights developments in inhomogeneous superconductivity, unconventional superconductivity and topological phases of superfluid 3 He, in which Andreev scattering and bound states underpin much of the physics of these systems. This article provides an introduction to the basic physics of Andreev scattering, bound-state formation and their signatures. The goal is both an introduction for interested readers who are not already experts in the field, and to highlight examples in which branch conversion scattering and Andreev bound states provide unique signatures in the transport properties of superconductors. This article is part of the theme issue ‘Andreev bound states’.

scholarly journals Fundamental dissipation due to bound fermions in the zero-temperature limit

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Autti ◽  
S. L. Ahlstrom ◽  
R. P. Haley ◽  
A. Jennings ◽  
G. R. Pickett ◽  
...  
Keyword(s):  
Critical Velocity ◽  
Ground State ◽  
Bound States ◽  
Bound State ◽  
Temperature Limit ◽  
Pair Breaking ◽  
Zero Temperature ◽  
Andreev Bound States ◽  
Macroscopic Object

Abstract The ground state of a fermionic condensate is well protected against perturbations in the presence of an isotropic gap. Regions of gap suppression, surfaces and vortex cores which host Andreev-bound states, seemingly lift that strict protection. Here we show that in superfluid 3He the role of bound states is more subtle: when a macroscopic object moves in the superfluid at velocities exceeding the Landau critical velocity, little to no bulk pair breaking takes place, while the damping observed originates from the bound states covering the moving object. We identify two separate timescales that govern the bound state dynamics, one of them much longer than theoretically anticipated, and show that the bound states do not interact with bulk excitations.

scholarly journals Andreev bound states in superconductor/ferromagnet point contact Andreev reflection spectra

2017 ◽  
Vol 95 (9) ◽  
Author(s):  
K. A. Yates ◽  
L. A. B. Olde Olthof ◽  
M. E. Vickers ◽  
D. Prabhakaran ◽  
M. Egilmez ◽  
...  
Keyword(s):  
Bound States ◽  
Andreev Reflection ◽  
Point Contact ◽  
Reflection Spectra ◽  
Andreev Bound States

scholarly journals Indirect searches for dark matter bound state formation and level transitions

2020 ◽  
Vol 9 (5) ◽  
Author(s):  
Iason Baldes ◽  
Francesca Calore ◽  
Kalliopi Petraki ◽  
Vincent Poireau ◽  
Nicholas L. Rodd
Keyword(s):  
Dark Matter ◽  
State Formation ◽  
Bound States ◽  
Bound State ◽  
Photon Mass ◽  
Dark Photon ◽  
Dissipation Of Energy ◽  
Light Force

Indirect searches for dark matter (DM) have conventionally been applied to the products of DM annihilation or decay. If DM couples to light force carriers, however, it can be captured into bound states via dissipation of energy that may yield detectable signals. We extend the indirect searches to DM bound state formation and transitions between bound levels, and constrain the emission of unstable dark photons. Our results significantly refine the predicted signal flux that could be observed in experiments. As a concrete example, we use Fermi-LAT dwarf spheroidal observations to obtain constraints in terms of the dark photon mass and energy which we use to search for the formation of stable or unstable bound states.

scholarly journals Spatial Rabi oscillations between Majorana bound states and quantum dots

2018 ◽  
Vol 9 ◽  
pp. 1527-1535
Author(s):  
Jun-Hui Zheng ◽  
Dao-Xin Yao ◽  
Zhi Wang
Keyword(s):  
Quantum Dot ◽  
Bound States ◽  
Bound State ◽  
Double Quantum ◽  
Energy Splitting ◽  
Rabi Oscillations ◽  
Andreev Bound States ◽  
Majorana Bound States ◽  
Nonlocal Quantum ◽  
Equal Amplitude

Background: A Majorana bound state is a superconducting quasiparticle that is the superposition of particle and hole with equal amplitude. We propose a verification of this amplitude equality by analyzing the spatial Rabi oscillations of the quantum states of a quantum dot that is tunneling-coupled to the Majorana bound states. Results: We find two resonant Rabi driving energies that correspond to the energy splitting due to the coupling of two spatially separated Majorana bound states. The resulting Rabi oscillating frequencies from these two different resonant driving energies are identical for the Majorana bound states, while different for ordinary Andreev bound states. We further study a double-quantum-dot setup and find a nonlocal quantum correlation between them that is mediated by two Majorana bound states. This nonlocal correlation has the signature of additional resonant driving energies. Conclusion: Our method can be used to distinguish between Majorana bound states and Andreev bound states. It also gives a precise measurement of the energy splitting between two Majorana bound states.

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.

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

2005 ◽  
Vol 19 (01n03) ◽  
pp. 495-497 ◽  
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.

scholarly journals Andreev reflection spectroscopy in transition metal oxides

2018 ◽  
Vol 376 (2125) ◽  
pp. 20150001
Author(s):  
Karen A. Yates ◽  
Lesley F. Cohen
Keyword(s):  
Transition Metal ◽  
Transition Metal Oxides ◽  
Bound States ◽  
Andreev Reflection ◽  
Transport Current ◽  
Reflection Spectroscopy ◽  
Theme Issue ◽  
Andreev Bound States ◽  
Current Spin Polarization

Here we review the literature concerning measurement of the Andreev reflection between a superconductor (S) and ferromagnet (F), with particular attention to the case where the ferromagnet is a transition metal oxide. We discuss the practicality of utilization of the current models for determination of the transport current spin polarization and examine the evidence for Andreev bound states. This article is part of the theme issue ‘Andreev bound states’.

scholarly journals Theory of Andreev bound states in S-F-S junctions and S-F proximity devices

2018 ◽  
Vol 376 (2125) ◽  
pp. 20150149 ◽  
Author(s):  
M. Eschrig
Keyword(s):  
Quantum Coherence ◽  
General Framework ◽  
Bound States ◽  
Hybrid Structures ◽  
Theme Issue ◽  
Josephson Devices ◽  
Andreev Bound States ◽  
Non Local ◽  
Metallic Parts ◽  
Strong Spin

Andreev bound states are an expression of quantum coherence between particles and holes in hybrid structures composed of superconducting and non-superconducting metallic parts. Their spectrum carries important information on the nature of the pairing, and determines the current in Josephson devices. Here, I focus on Andreev bound states in systems involving superconductors and ferromagnets with strong spin-polarization. I provide a general framework for non-local Andreev phenomena in such structures in terms of coherence functions, and show how the latter link wave function and Green-function based theories. This article is part of the theme issue ‘Andreev bound states’.

Absence of Andreev bound states inβ−PdBi2probed by point-contact Andreev reflection spectroscopy

2016 ◽  
Vol 94 (2) ◽  
Author(s):  
Liqiang Che ◽  
Tian Le ◽  
C. Q. Xu ◽  
X. Z. Xing ◽  
Zhixiang Shi ◽  
...  
Keyword(s):  
Bound States ◽  
Andreev Reflection ◽  
Point Contact ◽  
Reflection Spectroscopy ◽  
Andreev Bound States

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
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