1,313 research outputs found
Electron-Phonon Interaction and Ultrasonic Attenuation in the Ruthenate and Cuprate superconductors
This article derives an electron-phonon interaction suitable for interpreting
ultrasonic attenuation measurements in the ruthenate and cuprate
superconductors. The huge anisotropy found experimentally (Lupien et al., 2001)
in Sr2RuO4 in the normal state is accounted for in terms of the layered
square-lattice structure of Sr2RuO4, and the dominant contribution to the
attenuation in Sr2RuO4 is found to be due to electrons in the gamma band. The
experimental data in the superconducting state is found to be inconsistent with
vertical lines nodes in the gap in either (100) or (110) planes. Also, a
general method, based on the use of symmetry, is developed to allow for the
analysis of ultrasonic attenuation experiments in superconductors in which the
electronic band structure is complicated or not known. Our results, both for
the normal-state anisotropy, and relating to the positions of the gap nodes in
the superconducting state, are different from those obtained from analyses
using a more traditional model for the electron-phonon interaction in terms of
an isotropic electron stress tensor. Also, a brief discussion of the ultrasonic
attenuation in UPt3 is given.Comment: 12 pages. Comments have been added to the original version of this
article showing how, for the ultrasonic attenuation for a hexagonal crystal
(which must be isotropic with respect to rotations about the c axis) our
approach reproduces the results of the traditional isotropic electron stress
tensor mode
Ultrasonic attenuation in clean d-wave superconductors
We consider the attenuation of longitudinal ultrasonic waves in a clean
two-dimensional d-wave superconductor. We show that the attenuation coefficient
is linear in temperature at low temperatures for all in-plane directions of the
propagation of the ultrasound, and that the coefficient of the linear term can
be used to determine the parameters crucial for the low temperature transport
in these compounds.Comment: 4 pages, very minor changes, published versio
Ultrasonic Attenuation in Clean d-Wave Superconductors
We calculate the low temperature longitudinal ultrasonic attenuation rate
in clean d-wave superconductors. We consider the contribution of
previously ignored processes involving the excitation of a pair of quasi-holes
or quasi-particles. These processes, which are forbidden by energy conservation
in conventional s-wave superconductors, have a finite phase space in d-wave
superconductors due to the presence of nodes in the gap which give rise to soft
low-energy electronic excitations. We find the contribution to from
these processes to be proportional to in the regime ,(ultra-low temperature regime) and to be proportional to 1/T in
the region , (low temperature regime) where is the ultrasound wave-vector and is the maximum gap amplitude.
We explicitly evaluate these terms, for parameters appropriate to the cuprates,
for along the nodal and the antinodal directions and compare it with
the contribution from processes considered earlier(I.Vekhter et al {\it Phys.
Rev.}{\bf B59}, 7123(1999)). In the ultra-low temperature regime, the processes
considered by us make a contribution which is smaller by about a factor of 10
for along the nodal direction, while along the antinodal direction it
is larger by a factor of 100 or so. In the low temperature regime on the other
hand the contribution made by these terms is small. However taken together with
the original terms we describe a possible way to evaluate the parameter
.Comment: 9 pages, RevTex, accepted for publication in Physica
Ultrasonic Attenuation in the Vortex State of d-wave Superconductors
We calculate the low temperature quasi-particle contribution to the
ultrasonic attenuation rate in the mixed state of d-wave superconductors. Our
calculation is performed within the semi-classical approximation using
quasi-particle energies that are Doppler shifted, with respect to their values
in the Meissner phase, by the supercurrent associated with the vortices. We
find that the attenuation at low temperatures and at fields has a temperature independent contribution which is proportional to
where is the applied magnetic field. We indicate how our result
in combination with the zero-field result for ultrasonic attenuation can be
used to calculate one of the parameters , or given the
values for any two of them.Comment: 10 pages, RevTeX, submitted to Physica
BCS Model in Tsallis' Statistical Framework
We show that there is an effect of nonextensivity acting upon the BCS model
for superconductors in the ground state that motivates its study in the
Tsallis' statistical framework. We show that the weak-coupling limit
superconductors are well described by , where q is a real parameter
which characterizes the degree of nonextensivity of the Tsallis' entropy.
Nevertheless, small deviations with respect to q = 1 provide better agreement
when compared with experimental results. To illustrate this point, making use
of an approximated Fermi function, we show that measurements of the specific
heat, ultrasonic attenuation and tunneling experiments for tin (Sn) are better
described with q = 0.99.Comment: 13 pages, amssym
Ultrasound attenuation in gap-anisotropic systems
Transverse ultrasound attenuation provides a weakly-coupled probe of momentum
current correlations in electronic systems. We develop a simple theory for the
interpretation of transverse ultrasound attenuation coefficients in systems
with nodal gap anisotropy. Applying this theory we show how ultrasound can
delineate between extended-s and d-wave scenarios for the cuprate
superconductors.Comment: Uuencode file: 4 pages (Revtex), 3 figures. Some references adde
Determining the superconducting gap structure in Sr2RuO4 from sound attenuation studies below Tc
This work presents a quantitative theoretical study of the sound attenuation
in the unconventional multiband superconductor Sr2RuO4 below the
superconducting transition temperature Tc. Sound attenuation in this material
is shown to have the remarkable property of being able to identify different
nodal structures on different bands. The nodal structures on the \gamma band on
the one hand, and on the \alpha and \beta bands on the other, are both found to
be characterized by the existence of point nodes, but are significantly
different in their quantitative aspects.Comment: 7 pages, REVTe
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