591 research outputs found
Magnus force and acoustic Stewart-Tolman effect in type II superconductors
At zero magnetic field we have observed an electromagnetic radiation from
superconductors subjected by a transverse elastic wave. This radiation has an
inertial origin, and is a manifestation of the acoustic Stewart-Tolman effect.
The effect is used for implementing a method of measurement of an effective
Magnus force in type II superconductors. The method does not require the flux
flow regime and allows to investigate this force for almost the whole range of
the existence of the mixed state. We have studied behavior of the gyroscopic
force in nonmagnetic borocarbides and Nb. It is found that in borocarbides the
sign of the gyroscopic force in the mixed state is the same as in the normal
state, and its value (counted for one vortex of unit length) has only a weak
dependence on the magnetic field. In Nb the change of sign of the gyroscopic
force under the transition from the normal to the mixed state is observed.Comment: 4 pages, 5 figure
Non-dissipative drag of superflow in a two-component Bose gas
A microscopic theory of a non-dissipative drag in a two-component superfluid
Bose gas is developed. The expression for the drag current in the system with
the components of different atomic masses, densities and scattering lengths is
derived. It is shown that the drag current is proportional to the square root
of the gas parameter. The temperature dependence of the drag current is studied
and it is shown that at temperature of order or smaller than the interaction
energy the temperature reduction of the drag current is rather small. A
possible way of measuring the drag factor is proposed. A toroidal system with
the drag component confined in two half-ring wells separated by two Josephson
barriers is considered. Under certain condition such a system can be treated as
a Bose-Einstein counterpart of the Josephson charge qubit in an external
magnetic field. It is shown that the measurement of the difference of number of
atoms in two wells under a controlled evolution of the state of the qubit
allows to determine the drag factor.Comment: 13 pages, 3 figures. This preprint is extended and substantially
revised variant of related preprint cond-mat/040456
Study of magnetoelastic interaction in MnF by the acoustoelectric transformation method
The mechanisms of magnetoelastic interaction in MnF are studied using the
method of acoustoelectric transformation. The temperature dependence of the
piezomagnetic coupling coefficient and its anisotropy are determined in the
antiferromagnetic phase. We observe a new effect consisting in the appearance
of a non-diagonal component of the magnetic susceptibility tensor, which is
proportional to the square of the order parameter, under the action of the
shear wave. A phenomenological interpretation of the effect, which takes into
account a small-angle rotation of the crystal lattice, is presented. In the
paramagnetic state, the effect of acoustic deformation is reduced to the
modulation of the diagonal component of the susceptibility tensor
Acoustic characteristics of FeSe single crystals Acoustic characteristics of FeSe single crystals
The results of the comprehensive ultrasonic research of high quality single
crystals of FeSe are presented. Absolute values of sound velocities and their
temperature dependences were measured; elastic constants and Debye temperature
were calculated. The elastic C11-C12 and C11 constants undergo significant
softening under the structural tetra-ortho transformation. The significant
influence of the superconducting transition on the velocity and attenuation of
sound was revealed and the value of the superconducting energy gap was
estimated.Comment: 5 pages, 7 figures, 1 tabl
Elastic anomalies in HoNi2B2C single crystals
We have measured temperature and magnetic field dependencies of the sound
velocities and the sound attenuation in HoNi2B2C single crystals. The main
result is a huge softening the velocity of C66 mode due to a cooperative
Jahn-Teller effect, resulting in a tetragonal-orthorhombic structural phase
transition. Anomalies in the behavior of the C66 mode through various magnetic
phase transitions permit us to revise the low temperature H-T phase diagrams of
this compound.Comment: v2: a discussion of the C44 mode with the comparison to Y borocarbide
was adde
Characteristics of the electric field accompanying a longitudinal acoustic wave in a metal. Anomaly in the superconducting phase
The temperature dependence of the amplitude and phase of the electric
potential arising at a plane boundary of a conductor when a longitudinal
acoustic wave is incident normally on it is investigated theoretically and
experimentally. The surface potential is formed by two contributions, one of
which is spatially periodic inside the sample, with the period of the acoustic
field; the second is aperiodic and arises as a result of an additional
nonuniformity of the electron distribution in a surface layer of the metal. In
the nonlocal region the second contribution is dominant. The phases of these
contributions are shifted by approximately \pi /2. For metals in the normal
state the experiment is in qualitative agreement with the theory. The
superconducting transition is accompanied by catastrophically rapid vanishing
of the electric potential, in sharp contrast to the theoretical estimates,
which predict behavior similar to the BCS dependence of the attenuation
coefficient for a longitudinal sound.Comment: 9 pages, 6 figure
Critical currents and giant non-dissipative drag for superfluid electron-hole pairs in quantum Hall multilayers
Superfluid properties of electron-hole pairs in a quantum Hall four-layer
system are investigated. The system is considered as a solid state realization
of a two-component superfluid Bose gas with dipole-dipole interaction. One
superfluid component is formed in the top bilayer and the other component - in
the bottom one. We obtain the dispersion equation for the collective mode
spectrum and compute the critical parameters (the critical interlayer distance
and the critical currents) versus the filling factor. We find that the critical
currents of the components depend on each other. The maximum critical current
of a given component can be reached if the current of the other component is
equal to zero. The non-dissipative drag effect between the components is
studied. It is shown that in the system considered the drag factor is very
large. Under appropriate conditions it can be about 10 per sent, that is at
least in three order larder than one predicted for two-component atomic Bose
gases.Comment: 18 pages, 7 figure
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