9 research outputs found
Comment on the anisotropic impurity scattering in superconductors
We discuss a case of a strong anisotropic impurity scattering within the
model introduced in our previous paper [Phys. Rev. B54, 15463 (1996)] and
clarify our former statement about a possible enhancement of the critical
temperature in this scattering regime. We show that for the anisotropy of the
impurity potential determined by the functions from the non-identity
irreducible representations of the crystal point group, the critical
temperature decreases with the impurity scattering rate which is consistent
with a generally understood role of disorder in superconductors.Comment: 6 pages, RevTe
The phase transition phenomena in anisotropic superconductors: effect of the orthorhombic crystal field and the potential impurity scattering
A combined effect of the orthorhombic crystal field and potential impurity
scattering on several superconducting states of a tetragonal symmetry is
studied within a weak-coupling mean field approach. It is shown that the
nonmagnetic impurities stabilize the states belonging to the identity
irreducible representation. The electronic specific heat jump at the phase
transition is analyzed. Its dependence on the potential scattering rate for
large impurity concentration is shown to be remarkably different for the states
with a nonzero value of the Fermi surface averaged order parameter than for
those with a vanishing one. In particular, very distinct signals from
d_{x^2-y^2} state in YBCO and d_{xy} state in BSCCO compound are predicted.
This effect may be used as a test for the presence of these states in the above
cuprates.Comment: 21 pages, 2 tables, RevTex, 12 PostScript figure
Effect of anisotropic impurity scattering in superconductors
We discuss the weak-coupling BCS theory of a superconductor with the
impurities, accounting for their anisotropic momentum-dependent potential. The
impurity scattering process is considered in the t-matrix approximation and its
influence on the superconducting critical temperature is studied in the Born
and unitary limit for a d- and (d+s)-wave superconductors. We observe a
significant dependence of the pair-breaking strength on the symmetry of the
scattering potential and classify the impurity potentials according to their
ability to alter T_c. A good agreement with the experimental data for Zn doping
and oxygen irradiation in the overdoped cuprates is found.Comment: 31 pages, RevTex, 15 PostScript figure
Role of anisotropic impurity scattering in anisotropic superconductors
A theory of nonmagnetic impurities in an anisotropic superconductor including
the effect of anisotropic (momentum-dependent) impurity scattering is given. It
is shown that for a strongly anisotropic scattering the reduction of the
pair-breaking effect of the impurities is large. For a significant overlap
between the anisotropy functions of the scattering potential and that of the
pair potential and for a large amount of anisotropic scattering rate in
impurity potential the superconductivity becomes robust vis a vis impurity
concentration. The implications of our result for YBCO high-temperature
superconductor are discussed.Comment: 14 pages, RevTeX, 5 PostScript figures, to be published in Phys. Rev.
B (December 1, 1996
Superconducting instability of a non-centrosymmetric system
The Fermi gas approach to the weak-coupling superconductivity in the non-centrosymmetric systems lead to a conclusion of an approximately spin-orbit coupling independent critical temperature of the singlet states as well as the triplet states defined by the order parameter aligned with the antisymmetric spin-orbit coupling vector. We indicate that the above results follow from a simplified approximation of a density of states by a constant Fermi surface value. Such a scenario does not properly account for the spin-split quasiparticle energy spectrum and reduces the spin-orbit coupling influence on superconductivity to the bare pair-breaking effect of a lifted spin degeneracy. Applying the tight-binding model, which captures the primary features of the spin-split energy band, i.e., its enhanced width and the spin-orbit coupling induced redistribution of the spectral weights in the density of states, we calculate the critical temperature of a non-centrosymmetric superconductor. We report a general tendency of the critical temperature to be suppressed by the antisymmetric spin-orbit coupling. We indicate that, the monotonic decrease of the critical temperature may be altered by the spin-orbit coupling induced van Hove singularities which, when driven to the Fermi level, generate maxima in the phase diagram. Extending our considerations to the intermediate-coupling superconductivity we point out that the spin-orbit coupling induced change of the critical temperature depends on the structure of the electronic energy band and both – the strength and symmetry of the pair potential. Finally, we discuss the mixed singlet-triplet state superconducting instability and establish conditions concerning the symmetry of the singlet and triplet counterparts as well as the range of the spin-orbit coupling energy which make such a phase transition possible