621 research outputs found
Competitive 0 and {\pi} states in S/F multilayers: multimode approach
We have investigated the critical temperature behavior in periodic
superconductor/ ferromagnet (S/F) multilayers as a function of the
ferromagnetic layer thickness and the interface transparency. The
critical temperature exhibits a damped oscillatory behavior in these
systems due to an exchange field in the ferromagnetic material. In this work we
have performed calculations using the self-consistent multimode approach,
which is considered to be exact solving method. Using this approach we have
derived the conditions of 0 or state realization in periodic S/F
multilayers. Moreover, we have presented the comparison between the single-mode
and multimode approaches and established the limits of applicability of the
single-mode approximation, frequently used by experimentalists
Antiferromagnetic resonances in superconductor-ferromagnet multilayers
In this work, we study magnetization dynamics in superconductor-ferromagnet
(S-F) thin-film multilayer. Theoretical considerations supported by the
broad-band ferromagnetic resonance spectroscopy reveal development of acoustic
and optic resonance modes in S-F multilayers at significantly higher
frequencies in comparison to the Kittel mode of individual F-layers. These
modes are formed due to antiferromagnetic-like interaction between F-layers via
shared circulating superconducting currents in S-layers. The gap between
resonance modes is determined by the thickness and superconducting penetration
depth in S-layers. Overall, rich spectrum of S-F multilayers and its tunability
opens wide prospects for application of these multialyers in magnonics as well
as in various superconducting hybrid systems.Comment: 5 pages, 4 figures, 34 reference
Double Fe-impurity charge state in the topological insulator BiSe
The influence of individual impurities of Fe on the electronic properties of
topological insulator BiSe is studied by Scanning Tunneling Microscopy.
The microscope tip is used in order to remotely charge/discharge Fe impurities.
The charging process is shown to depend on the impurity location in the
crystallographic unit cell, on the presence of other Fe impurities in the close
vicinity, as well as on the overall doping level of the crystal. We present a
qualitative explanation of the observed phenomena in terms of tip-induced local
band bending. Our observations evidence that the specific impurity neighborhood
and the position of the Fermi energy with respect to the Dirac point and bulk
bands have both to be taken into account when considering the electron
scattering on the disorder in topological insulators.Comment: 10 pages, accepted for publication in Applied Physics Letters, minor
bugs were correcte
Tight inequalities for nonclassicality of measurement statistics
In quantum optics, measurement statistics -- for example, photocounting
statistics -- are considered nonclassical if they cannot be reproduced with
statistical mixtures of classical radiation fields. We have formulated a
necessary and sufficient condition for such nonclassicality. This condition is
given by a set of inequalities that tightly bound the convex set of
probabilities associated with classical electromagnetic radiation. Analytical
forms for full sets and subsets of these inequalities are obtained for
important cases of realistic photocounting measurements and unbalanced homodyne
detection. As an example, we consider photocounting statistics of
phase-squeezed coherent states. Contrary to a common intuition, the analysis
developed here reveals distinct nonclassical properties of these statistics
that can be experimentally corroborated with minimal resources.Comment: 12 pages, 4 figure
Reentrant superconductivity in proximity to a topological insulator
In the following paper we investigate the critical temperature behavior
in the two-dimensional S/TI (S denotes superconductor and TI - topological
insulator) junction with a proximity induced in-plane helical magnetization in
the TI surface. The calculations of are performed using the general
self-consistent approach based on the Usadel equations in Matsubara Green's
functions technique. We show that the presence of the helical magnetization
leads to the nonmonotonic behavior of the critical temperature as a function of
the topological insulator layer thickness.Comment: submitted to Physical Review
Spectroscopic evidence for strong correlations between local superconducting gap and local Altshuler-Aronov density-of-states suppression in ultrathin NbN films
Disorder has different profound effects on superconducting thin films. For a
large variety of materials, increasing disorder reduces electronic screening
which enhances electron-electron repulsion. These fermionic effects lead to a
mechanism described by Finkelstein: when disorder combined to electron-electron
interactions increases, there is a global decrease of the superconducting
energy gap and of the critical temperature , the ratio
/ remaining roughly constant. In addition, in most films an
emergent granularity develops with increasing disorder and results in the
formation of inhomogeneous superconducting puddles. These gap inhomogeneities
are usually accompanied by the development of bosonic features: a pseudogap
develops above the critical temperature and the energy gap
starts decoupling from . Thus the mechanism(s) driving the appearance of
these gap inhomogeneities could result from a complicated interplay between
fermionic and bosonic effects. By studying the local electronic properties of a
NbN film with scanning tunneling spectroscopy (STS) we show that the
inhomogeneous spatial distribution of is locally strongly correlated
to a large depletion in the local density of states (LDOS) around the Fermi
level, associated to the Altshuler-Aronov effect induced by strong electronic
interactions. By modelling quantitatively the measured LDOS suppression, we
show that the latter can be interpreted as local variations of the film
resistivity. This local change in resistivity leads to a local variation of
through a local Finkelstein mechanism. Our analysis furnishes a purely
fermionic scenario explaining quantitatively the emergent superconducting
inhomogeneities, while the precise origin of the latter remained unclear up to
now.Comment: 11 pages, 4 figure
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