579 research outputs found
Local density of states around single vortices and vortex pairs: effect of boundaries and hybridization of vortex core states
The profiles of local density of states (LDOS) around different vortex
configurations in mesoscopic superconductors are studied taking account of the
interference of quasiparticle waves experiencing Andreev reflection within the
vortex cores and normal reflection at the boundaries or defects. For subgap
energy levels these interference effects reveal themselves in a nontrivial
dependence of the positions of the LDOS peaks on the intervortex distance and
sample size: the peak positions generally do not coincide with the
superconducting phase singularity points. The LDOS profiles are calculated for
three generic examples: (i) vortex-vortex pair; (ii) vortex positioned near a
flat boundary; (iii) vortex positioned in the center of a superconducting disk.
The resulting evolution of the Andreev interference patterns could be
observable by scanning tunneling spectroscopy techniques.Comment: 9 pages, 6 figure
Abrikosov vortex escape from a columnar defect as a topological electronic transition in vortex core
We study microscopic scenario of vortex escape from a columnar defect under
the influence of a transport current. For defect radii smaller than the
superconducting coherence length the depinning process is shown to be a
consequence of two subsequent topological electronic transitions in a trapped
vortex core. The first transition at a critical current is associated
with the opening of Fermi surface segments corresponding to the creation of a
vortex--antivortex pair bound to the defect. The second transition at a certain
current is caused by merging of different Fermi surface segments,
which accompanies the formation of a freely moving vortex.Comment: 5 pages, 4 figure
Resonance energy and charge pumping through quantum SINIS contacts
We propose a mechanism of quantum pumping mediated by the spectral flow in a
voltage-biased SINIS quantum junction and realized via the sequential closing
of the minigaps in the energy spectrum in resonance with the Josephson
frequency. We show that the dc current exhibits giant peaks at rational
voltages
FFLO states and quantum oscillations in mesoscopic superconductors and superfluid ultracold Fermi gases
We have studied the distinctive features of the
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) instability and phase transitions in
two--dimensional (2D) mesoscopic superconductors placed in magnetic field of
arbitrary orientation and rotating superfluid Fermi gases with imbalanced state
populations. Using a generalized version of the phenomenological
Ginzburg-Landau theory we have shown that the FFLO states are strongly modified
by the effect of the trapping potential confining the condensate. The
phenomenon of the inhomogeneous state formation is determined by the interplay
of three length scales: (i) length scale of the FFLO instability; (ii) 2D
system size; (iii) length scale associated with the orbital effect caused
either by the Fermi condensate rotation or magnetic field component applied
perpendicular to the superconducting disc. We have studied this interplay and
resulting quantum oscillation effects in both superconducting and superfluid
finite -- size systems with FFLO instability and described the hallmarks of the
FFLO phenomenon in a restricted geometry. The finite size of the system is
shown to affect strongly the conditions of the observability of switching
between the states with different vorticities.Comment: 11 pages, 5 figures, Submitted to PR
Multiple Vortex Cores in 2D Electronic Systems with Proximity Induced Superconductivity
The structure of a proximity induced vortex core in a two-dimensional (2D)
metallic layer covering a superconducting half-space is calculated. We predict
formation of a multiple vortex core characterized by two-scale behavior of the
local density of states (LDOS). For coherent tunnelling between the 2D layer
and the bulk superconductor, the spectrum has two subgap branches while for
incoherent tunnelling only one of them remains. The resulting splitting of the
zero-bias anomaly and the multiple peak structure in the LDOS should be visible
in the tunnelling spectroscopy experiments.Comment: 13 pages, 4 figure
Single-electron transport through the vortex core levels in clean superconductors
We develop a microscopic theory of single-electron transport in N-S-N hybrid
structures in the presence of applied magnetic field introducing vortex lines
in a superconductor layer. We show that vortex cores in a thick and clean
superconducting layer are similar to mesoscopic conducting channels where the
bound core states play the role of transverse modes. The transport through not
very thick layers is governed by another mechanism, namely by resonance
tunneling via vortex core levels. We apply our method to calculation of the
thermal conductance along the magnetic field.Comment: 4 pages, 1 figur
Giant Mesoscopic Fluctuations and Long-Range Superconducting Correlations in Superconductor-Ferromagnet Structures
International audienceThe fluctuating superconducting correlations emerging in dirty hybrid structures under the conditions of the strong proximity effect are demonstrated to affect the validity range of the widely used formalism of Usadel equations at mesoscopic scales. In superconductor ferromagnet structures these giant mesoscopic fluctuations originating from the interference effects for the Cooper pair wave function in the presence of the exchange field can be responsible for an anomalously slow decay of superconducting correlations in a ferromagnet even when the noncollinear and spin orbit effects are negligible. The resulting sample to sample fluctuations of the Josephson current in superconductor ferromagnetic superconductor junctions and the local density of states in superconductor ferromagnetic hybrid structures can provide an explanation of the long range proximity phenomena observed in mesoscopic samples with collinear magnetization
Dephasing time and magnetoresistance of two-dimensional electron gas in spatially modulated magnetic fields
The effect of a spatially modulated magnetic field on the weak localization
phenomenon in two-dimensional electron gas (2DEG) is studied. Both the
dephasing time and magnetoresistance are shown to reveal a nontrivial
behavior as functions of the characteristics of magnetic field profiles. The
magnetic field profiles with rather small spatial scales and modulation
amplitudes such that are characterized by the
dephasing rate . The increase in the flux value
results in a crossover to a standard linear dependence
. Applying an external homogeneous magnetic field
one can vary the local dephasing time in the system and affect the resulting
average transport characteristics. We have investigated the dependence of the
average resistance vs the field for some generic systems and predict a
possibility to observe a positive magnetoresistance at not too large
values. The resulting dependence of the resistance vs should reveal a peak
at the field values .Comment: 12 pages, 5 figure
Higgs modes in proximized superconducting systems
The proximity effect in hybrid superconducting–normal-metal structures is shown to affect strongly the coherent oscillations of the superconducting order parameter known as the Higgs modes. The standard Higgs mode at frequency is damped exponentially by the quasiparticle leakage from the primary superconductor. Two new Higgs modes with the frequencies depending on both the primary and induced gaps in the hybrid structure are shown to appear due to the coherent electron transfer between the superconductor and the normal metal. Altogether, these three modes determine the long-time asymptotic behavior of the superconducting order parameter disturbed either by the electromagnetic pulse or the quench of the system parameters and thus are of crucial importance for the dynamical properties and restrictions on the operating frequencies for superconducting devices based on the proximity effect used, e.g., in quantum computing, in particular, with topological low-energy excitations
Vanishing Meissner effect as a hallmark of in-plane FFLO instability in superconductor - ferromagnet layered systems
We demonstrate that in a wide class of multilayered superconductor -
ferromagnet structures (e.g., S/F, S/F/N and S/F/F') the vanishing Meissner
effect signals the appearance of the in-plane Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) modulated superconducting phase. In contrast to the bulk superconductors
the FFLO instability in these systems can emerge at temperatures close to the
critical one and is effectively controlled by the S layer thickness and the
angle between magnetization vectors in the F/F' bilayers. The predicted FFLO
state reveals through the critical temperature oscillations vs the
perpendicular magnetic field component.Comment: 5 pages, 5 figure
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