266 research outputs found
NMR relaxation rate in non-centrosymmetric superconductors
The spin-lattice relaxation rate of nuclear magnetic resonance in a clean
superconductor without inversion center is calculated for arbitrary pairing
symmetry and band structure, in the presence of strong spin-orbit coupling.Comment: 4 page
Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions
We compute the frequency and magnetic field dependencies of the reflectivity
in layered superconductors with two alternating intrinsic Josephson
junctions with different critical current densities and quasiparticle
conductivities for the electric field polarized along the c-axis. The parameter
describing the electronic compressibility of the layers and the charge
coupling of neighboring junctions was extracted for the
SmLaSrCuO superconductor from two independent
optical measurements, the fit of the loss function at zero magnetic
field and the magnetic field dependence of the peak positions in .
The experiments are consistent with a free electron value for near
the Josephson plasma frequencies.Comment: 4 pages, 4 postscript figures, misprints in table correcte
Quantum fluctuations in Larkin-Ovchinnikov-Fulde-Ferrell superconductors
We study the superconducting order parameter fluctuations near the phase
transition into the Larkin-Ovchinnikov-Fulde-Ferrell state in the clean limit
at zero temperature. In contrast to the usual normal metal-to-uniform
superconductor phase transition, the fluctuation corrections are dominated by
the modes with the wave vectors away from the origin. We find that the
superconducting fluctuations lead to a divergent spin susceptibility and a
breakdown of the Fermi-liquid behavior at the quantum critical point.Comment: 10 pages, 4 figure
Fermion Analogy for Layered Superconducting Films in Parallel Magnetic Field
The equivalence between the Lawrence-Doniach model for films of extreme
type-II layered superconductors and a generalization of the back-scattering
model for spin-1/2 electrons in one dimension is demonstrated. This fermion
analogy is then exploited to obtain an anomalous tail for
the parallel equilibrium magnetization of the minimal double layer case in the
limit of high parallel magnetic fields for temperatures in the
critical regime.Comment: 11 pages of plain TeX, 1 postscript figur
Enhanced superconducting proximity effect in clean ferromagnetic domain structures
We investigate the superconducting proximity effect in a clean magnetic
structure consisting of two ferromagnetic layered domains with antiparallel
magnetizations in contact with a superconductor. Within the quasiclassical
Green's function approach we find that the penetration of the superconducting
correlations into the magnetic domains can be enhanced as compared to the
corresponding single domain structure. This enhancement depends on an effective
exchange field which is determined by the thicknesses and the exchange fields
of the two domains. The pair amplitude function oscillates spatially inside
each domain with a period inversely proportional to the local exchange field.
While the oscillations have a decreasing amplitude with distance inside the
domain which is attached to the superconductor, they are enhancing in the other
domain and can reach the corresponding normal metal value for a zero effective
exchange field. We also find that the corresponding oscillations in the Fermi
level proximity density of states as a function of the second domain's
thickness has an growing amplitude over a range which depends on the effective
exchange field. Our findings can be explained as the result of cancellation of
the exchange fields induced phases gained by an electron inside the two domains
with antiparallel magnetizations.Comment: 7 pages, 4 figure
On the spin susceptibility of noncentrosymmetric superconductors
We calculate the spin susceptibility of a superconductor without inversion
symmetry, both in the clean and disordered cases. The susceptibility has a
large residual value at zero temperature, which is further enhanced in the
presence of scalar impurities.Comment: 12 pages, 3 figure
Inhomogeneous ground state and the coexistence of two length scales near phase transitions in real solids
Real crystals almost unavoidably contain a finite density of dislocations. We
show that this generic type of long--range correlated disorder leads to a
breakdown of the conventional scenario of critical behavior and standard
renormalization group techniques based on the existence of a simple,
homogeneous ground state. This breakdown is due to the appearance of an
inhomogeneous ground state that changes the character of the phase transition
to that of a percolative phenomenon. This scenario leads to a natural
explanation for the appearance of two length scales in recent high resolution
small-angle scattering experiments near magnetic and structural phase
transitions.Comment: 4 pages, RevTex, no figures; also available from
http://www.tp3.ruhr-uni-bochum.de/archive/tpiii_archive.htm
High quality ferromagnetic 0 and pi Josephson tunnel junctions
We fabricated high quality \Nb/\Al_2\O_3/\Ni_{0.6}\Cu_{0.4}/\Nb
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Depending on the thickness of the ferromagnetic \Ni_{0.6}\Cu_{0.4} layer and
on the ambient temperature, the junctions were in the 0 or ground state.
All junctions have homogeneous interfaces showing almost perfect Fraunhofer
patterns. The \Al_2\O_3 tunnel barrier allows to achieve rather low damping,
which is desired for many experiments especially in the quantum domain. The
McCumber parameter increases exponentially with decreasing
temperature and reaches at . The critical
current density in the state was up to at , resulting in a Josephson penetration depth as low as
. Experimentally determined junction parameters are well
described by theory taking into account spin-flip scattering in the
\Ni_{0.6}\Cu_{0.4} layer and different transparencies of the interfaces.Comment: Changed content and Corrected typo
Bichiral structure of feroelectric domain wall driven by flexoelectricity
The influence of flexoelectric coupling on the internal structure of neutral
domain walls in tetragonal phase of perovskite ferroelectrics is studied. The
effect is shown to lower the symmetry of 180-degree walls which are oblique
with respect to the cubic crystallographic axes, while {100} and {110} walls
stay "untouched". Being of the Ising type in the absence of the flexoelectric
interaction, the oblique domain walls acquire a new polarization component with
a structure qualitatively different from the classical Bloch-wall structure. In
contrast to the Bloch-type walls, where the polarization vector draws a helix
on passing from one domain to the other, in the flexoeffect-affected wall, the
polarization rotates in opposite directions on the two sides of the wall and
passes through zero in its center. Since the resulting polarization profile is
invariant upon inversion with respect to the wall center it does not brake the
wall symmetry in contrast to the classical Bloch-type walls. The flexoelectric
coupling lower the domain wall energy and gives rise to its additional
anisotropy that is comparable to that conditioned by the elastic anisotropy.
The atomic orderof- magnitude estimates shows that the new polarization
component P2 may be comparable with spontaneous polarization Ps, thus
suggesting that, in general, the flexoelectric coupling should be mandatory
included in domain wall simulations in ferroelectrics. Calculations performed
for barium titanate yields the maximal value of the P2, which is much smaller
than that of the spontaneous polarization. This smallness is attributed to an
anomalously small value of a component of the "strain-polarization"
elecrostictive tensor in this material
Novel ordering of an S = 1/2 quasi one-dimensional Ising-like anitiferromagnet in magnetic field
High-field specific heat measurements on BaCo2V2O8, which is a good
realization of an S = 1/2 quasi one-dimensional Ising-like antifferomagnet,
have been performed in magnetic fields up to 12 T along the chain and at
temperature down to 200 mK. We have found a new magnetic ordered state in the
field-induced phase above Hc ~ 3.9 T. We suggest that a novel type of the
incommensurate order, which has no correspondence to the classical spin system,
is realized in the field-induced phase.Comment: 4pages, 4figure
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