共查询到20条相似文献,搜索用时 31 毫秒
1.
L. Alff S. Kleefisch U. Schoop M. Zittartz T. Kemen T. Bauch A. Marx R. Gross 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):423-438
Andreev bound states at the surface of superconductors are expected for any pair potential showing a sign change in different
k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report
on the observation of Andreev bound states in high temperature superconductors (HTS) employing tunneling spectroscopy on bicrystal
grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic
field. The tunneling spectra of GBJ formed by YBa2Cu3O (YBCO), Bi2Sr2CaCu2O(BSCCO), and La1.85Sr0.15CuO4 (LSCO) show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy
that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS Nd1.85Ce0.15CuO4-y (NCCO) no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero
to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev
bound states are discussed and experimental evidence for anomalous Meissner currents is presented.
Received: 17 February 1998 / Revised: 27 April 1998 / Accepted: 23 June 1998 相似文献
2.
Diego A. Manjarrs William J. Herrera Shirley Gmez 《Physica B: Condensed Matter》2009,404(18):2799-2801
In order to consider the Dirac-like spectrum of graphene we employ the Bogoliubov de Gennes–Dirac formalism to determine the quasiparticle Andreev levels in an NS surface (normal–superconductor). The normal region is characterized by a width L while the superconducting region is semi-infinite and both regions are made of doped graphene. The quasiparticle energy spectrum is originated by the Andreev reflections that occur in the NS interface. It is shown that this spectrum depends on the width of the normal region and the Fermi energy in each region. When the Fermi energy in the normal metal is lower than the gap of the superconductor region, the spectrum is affected by specular Andreev reflections. The equation that is obtained to find the spectrum is very general and we solve it for some particular cases. We find that the energy spectrum oscillates when the Fermi energy in graphene is changed. Finally we obtain under some approximations an equation for the energy spectrum which is similar in structure as those obtained for an INS conventional junction. 相似文献
3.
Ya. G. Ponomarev S. A. Kuzmichev M. G. Mikheev M. V. Sudakova S. N. Tchesnokov T. E. Shanygina O. S. Volkova A. N. Vasiliev Th. Wolf 《Journal of Experimental and Theoretical Physics》2011,113(3):459-467
Current-voltage characteristics (CVCs) of Andreev superconductor-constriction-superconductor (ScS) contacts in polycrystalline
samples of FeSe with the critical temperature T
C = (12 ± 1) K have been measured using the break-junction technique. In Sharvin-type nanocontacts, two sets of subharmonic
gap structures were detected due to multiple Andreev reflections, indicating the existence of two nodeless superconducting
gaps Δ
L
= (2.75 ± 0.3) meV and Δ
S
= (0.8 ± 0.2) meV. Well-shaped CVCs for stacks of Andreev contacts with up to five contacts were observed due to the layered
structure of FeSe (the intrinsic multiple Andreev reflections effect). An additional fine structure in the CVCs of Andreev
ScS nanocontacts is attributed to the existence of a Leggett mode. A linear relation between the superconducting gap Δ
L
and the magnetic resonance energy E
magres ≈ 2Δ
L
is found to be valid for layered iron pnictides. 相似文献
4.
Herbert Kroemer 《Superlattices and Microstructures》1999,25(5-6)
A simple one-dimensional model for SNS weak links in the ballistic limit is presented. In the presence of a bias voltage, the quasiparticle state at any given instant of time is described as a superposition of that particular set of phase-dependent Andreev bound states that belongs to the specific phase difference present at that instant between the superconducting banks. The treatment—basically a form of adiabatic perturbation theory—has a strong formal similarity to the treatment of the k -space dynamics of an electron in a periodic potential under perturbation by an external electric field, sufficiently strong to cause transitions across the energy gaps between bands (Zener tunneling). It is shown that the quasiparticle wavefunction retains its phase information during analogous transitions between Andreev bands. The experimental observation of Shapiro steps at one-half the canonical voltage follows naturally from the model, along with some of the experimental properties of these steps, especially their much weaker temperature dependence, compared to the canonical steps. 相似文献
5.
We have studied the interplay of Andreev reflection and cyclotron motion of quasiparticles at a superconductor-normal-metal interface with a strong magnetic field applied parallel to the interface. Bound states are formed due to the confinement introduced by both the external magnetic field and the superconducting gap. These bound states are a coherent superposition of electron and hole edge excitations similar to those realized in finite quantum-Hall samples. We find the energy spectrum for these Andreev edge states and calculate transport properties. 相似文献
6.
A. M. Bobkov 《JETP Letters》2002,75(8):383-386
Low-temperature conductance peaks due to the surface Andreev bound states in SIN and SIS junctions with chiral superconductors are considered. It is shown that, in SIN junctions, the conductance as a function of voltage, G(V), is highly sensitive to the dependence of the barrier transparency on the direction of the quasiparticle momentum. A weak magnetic field applied to the junction shifts the conductance peaks. In symmetric SIS junctions, the presence of chiral levels of Andreev bound states on both sides of the barrier gives rise to a conductance peak at V=0. 相似文献
7.
Nondissipative Josephson current through nanoscale superconducting constrictions is carried by spectroscopically sharp energy states, the so-called Andreev states. Although theoretically predicted almost 40 years ago, no direct spectroscopic evidence of these Andreev bound states exists to date. We propose a novel type of spectroscopy based on embedding a superconducting constriction, formed by a single-level molecule junction, in a microwave QED cavity environment. In the electron-dressed cavity spectrum we find a polariton excitation at twice the Andreev bound state energy, and a superconducting-phase-dependent ac Stark shift of the cavity frequency. Dispersive measurement of this frequency shift can be used for Andreev bound state spectroscopy. 相似文献
8.
G. A. Gogadze 《Il Nuovo Cimento D》1988,10(12):1519-1524
Summary The effect of non-Josephson generation (high-frequency oscillations of voltage) in the resistive state of the superconducting
film is studied theoretically in the presence of a constant magnetic field. The density of the generation current in the magnetic
field is calculated. The consideration is based on the earlier developed model, in which the above effect is due to the bremsstrahlung
radiation from the particles with the energy ε>Δ which are injected from the quasi-normal layer of the phase slip centre to
the superconducting bank. The quasi-particles pick up the energy in the process of the multiple Andreev scattering at theN-S boundaries, and the bremsstrahlung radiation is only possible if ε-Δ is of the order of the perturbation energy of the off-diagonal
potential
at theN-S boundary (~ΔΓ
3/2, where γ is the depairing factor of the super-conductor). 相似文献
9.
Wagenknecht M Koelle D Kleiner R Graser S Schopohl N Chesca B Tsukada A Goennenwein ST Gross R 《Physical review letters》2008,100(22):227001
We use quasiparticle tunneling across La2-xCexCuO4 grain boundary junctions to probe the superconducting state and its disappearance with increasing temperature and magnetic field. A zero bias conductance peak due to zero energy surface Andreev bound states is a clear signature of the phase coherence of the superconducting state. Hence, such a peak must disappear at or below the upper critical field Bc2(T). For La2-xCexCuO4 this approach sets a lower bound for Bc2(0) approximately 25 T which is substantially higher than reported previously. The method of probing the superconducting state via Andreev bound states should also be applicable to other cuprate superconductors. 相似文献
10.
Spin Polarization and Andreev Conductance through a Diluted Magnetic Semiconductor Quantum Wire with Spin--Orbit Interaction 下载免费PDF全文
Spin-dependent Andreev reflection and spin polarization through a diluted magnetic semiconductor quantum wire coupled to normal metallic and superconductor electrodes are investigated using scattering theory. When the spin-orbit coupling is considered, more Andreev conductance steps appear at the same Fermi energy. Magnetic semiconductor quantum wire separates the spin-up and spin-down electrons. The Fermi energy, at which different- spin-state electrons begin to separate, becomes lower due to the effect of the spin-orbit interaction. The spin filter effect can be measured more easily by investigating the Andreev conductance than by investigating the normal conductance. 相似文献
11.
We examine the density of states of an Andreev billiard and show that any billiard with a finite upper cutoff in the path length distribution P(s) will possess an energy gap on the scale of the Thouless energy. An exact quantum mechanical calculation for different Andreev billiards gives good agreement with the semiclassical predictions when the energy dependent phase shift for Andreev reflections is properly taken into account. Based on this new semiclassical Bohr-Sommerfeld approximation of the density of states, we derive a simple formula for the energy gap. We show that the energy gap, in units of Thouless energy, may exceed the value predicted earlier from random matrix theory for chaotic billiards. 相似文献
12.
Spatial quantization of the energy spectrum of quasiparticles, bound by Andreev scattering in the normal layer of SNS junctions, remains observable in weak constant magnetic fieldsH
parallel to the phase boundaries. Quasiparticles, especially in the low lying Andreev states, can traverse thick normal regions many thousand times before they are scattered once by interaction withH
. This confirms the expectation that quasiparticle transport phenomena in superconducting heterostructures should be little influenced by magnetic fields as long as the cyclotron radius greatly exceeds the average spatial extension of the unperturbed wave functions normal to the phase boundaries. 相似文献
13.
A superconductor-topological insulator-superconductor (S/TI/S) junction having normal region at angle θ is studied theoretically to investigate the junction angle dependency of the Andreev reflection and the formation of the Andreev bound states in the step and planar S/TI/S structures. It is found that the Andreev reflection becomes θ dependent only in the presence of the potential barrier at the TI/S interface. In particular, the step and planar TI/S junction have totally different conductive behavior with bias voltage and potential barrier in the regime of retro and specular Andreev reflection. Interestingly, we find that the elliptical cross section of Dirac cone, an important feature of topological insulator with step surface defect, affects the Fabry-Perot resonance of the Andreev reflection induced Andreev bound states (which become Majorana zero energy states at low chemical potential) in the step S/TI/S structure. Unlike the usual planar S/TI/S structures, we find these ellipticity affected Andreev bound states lead to non-monotonic Josephson super-current in the step S/TI/S structure whose non-monotonicity can be controlled with the use of the potential barrier, which may find applications in nanoelectronics. 相似文献
14.
Václav Janiš Vladislav Pokorný Martin Žonda 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(9):197
Behavior of Andreev gap states in a quantum dot with Coulomb repulsion symmetricallyattached to superconducting leads is studied via the perturbation expansion in theinteraction strength. We find the exact asymptotic form of the spin-symmetric solution forthe Andreev states continuously approaching the Fermi level. We thereby derive a criticalinteraction at which the Andreev states at zero temperature merge at the Fermi energy,being the upper bound for the 0-π transition. We show that the spin-symmetricsolution becomes degenerate beyond this interaction, in the π phase, and the Andreevstates do not split unless the degeneracy is lifted. We further demonstrate that thedegeneracy of the spin-symmetric state extends also into the 0 phase in which the solutions with zero andnon-zero frequencies of the Andreev states may coexist. 相似文献
15.
Herv Courtois Philippe Gandit Bernard Pannetier Dominique Mailly 《Superlattices and Microstructures》1999,25(5-6)
We review the mesoscopic transport in a diffusive proximity superconductor made of a normal metal (N) in metallic contact with a superconductor (S). The Andreev reflection of electrons on the N–S interface is responsible for the diffusion of electron pairs in N. Superconducting-like properties are induced in the normal metal. In particular, the conductivity of the N metal is locally enhanced by the proximity effect. A re-entrance of the metallic conductance occurs when all the energies involved (e.g. temperature and voltage) are small. The relevant characteristic energy is the Thouless energy which is divided by the diffusion time for an electron travelling throughout the sample. In loop-shaped devices, a 1 / T temperature-dependent oscillation of the magnetoresistance arises with a large amplitude from the long-range coherence of low-energy pairs. 相似文献
16.
We investigated superconducting AuIn2 by point-contact spectroscopy. Andreev reflexion was observed with nearly full excess current at contact sizes down to 0.15
nm. This implies, together with a large superconducting coherence length of 11 μm, almost ideal retroreflectivity. At the
onset of lateral confinement of the ballistic electrons the Andreev-derived spectra broaden dramatically due to inelastic
scattering at defects or the strain field near the contact. Lateral confinement does not suppress Andreev reflexion. 相似文献
17.
B. P. Vodopyanov 《JETP Letters》2008,87(6):328-333
The Andreev reflection probability for a ferromagnet/isolator/superconductor (FIS) contact at the arbitrary spin-dependent
amplitudes of the electron waves transmitted through and reflected from the potential barrier is found. It is shown that the
Andreev reflection probabilities of electron and hole excitations in the FIS contact are different. The energy levels of the
Andreev bound states are found. The ballistic conductance of the point FIS contact is calculated.
The text was submitted by the author in English. 相似文献
18.
《Physics letters. A》2020,384(27):126694
We consider the edge of a superconducting topological insulator with the impurity in the presence of the Zeeman field. We analytically prove that in the trivial phase two Andreev bound states (ABSs) arise with energies moving from the superconducting gap edges to zero forming two Majorana-like bound states, as the impurity strength varies from 0 to ±2. When the Zeeman field is locally perturbed, ABSs arise both in the trivial and topological phases, but in the topological phase ABSs with energy near the gap edges cannot transform into Majorana bound states and vice versa. 相似文献
19.
We investigated superconducting AuIn2 by point-contact spectroscopy. Andreev reflexion was observed with nearly full excess current at contact sizes down to 0.15 nm. This implies, together with a large superconducting coherence length of 11 μm, almost ideal retroreflectivity. At the onset of lateral confinement of the ballistic electrons the Andreev-derived spectra broaden dramatically due to inelastic scattering at defects or the strain field near the contact. Lateral confinement does not suppress Andreev reflexion. 相似文献
20.
We investigated transport in Nb-InAs hybrid structures in perpendicular magnetic fields up to the quantum Hall regime. Due
to the high contact quality of our samples, Andreev reflection dominates the transport properties in a range of experimental
parameters. Our experiments were performed on periodic arrays of Nb filled stripes or antidots in an InAs-based 2DEG. According
to geometry and field strength we observe the following effects: At low fields, up to a few flux quanta per unit cell, we
find phase-coherent behavior, such as flux-periodic oscillations. At slightly higher fields, the Andreev reflection probability
is determined by induced superconductivity in the 2DEG, which is gradually suppressed by an increasing magnetic field. In
the arrays of Nb filled antidots we find that the commensurability peaks are suppressed since Andreev reflection restores
regular motion in velocity space. Due to the high critical field of the Nb nanostructures, we can also enter the edge state
regime, where we observe a pronounced increase of the amplitude of 1/B-periodic magnetoresistance oscillations. The latter
can be traced to an enhanced backscattering of Andreev-reflected edge channels, which contain both electrons and holes.
PACS 74.45.+c; 73.43.Qt; 73.63.-b 相似文献