4,988 research outputs found
Scaling of Coulomb pseudo-potential in s-wave narrow-band superconductors
The Coulomb pseudo-potential is extracted by fitting the numerically
calculated transition temperature of the Eliashberg-Nambu equation which
is extended to incorporate the narrow-band effects, that is, the vertex
correction and the frequency dependence of the screened Coulomb interaction. It
is shown that even for narrow-band superconductors, where the fermi energy is comparable with the phonon frequency , the Coulomb
pseudo-potential is a pertinent parameter, and is still given by , provided is
appropriately scaled.Comment: 5 pages, 3 figures, accepted for publication by Phys. Rev.
The dynamically induced Fermi arcs and Fermi pockets in two dimensions: a model for underdoped cuprates
We investigate the effects of the dynamic bosonic fluctuations on the Fermi
surface reconstruction in two dimensions as a model for the underdoped
cuprates. At energies larger than the boson energy , the dynamic
nature of the fluctuations is not important and the quasi-particle dispersion
exhibits the shadow feature like that induced by a static long range order. At
lower energies, however, the shadow feature is pushed away by the finite
. The detailed low energy features are determined by the bare
dispersion and the coupling of quasi-particles to the dynamic fluctuations. We
present how these factors reconstruct the Fermi surface to produce the Fermi
arcs or the Fermi pockets, or their coexistence. Our principal result is that
the dynamic nature of the fluctuations, without invoking a
yet-to-be-established translational symmetry breaking hidden order, can produce
the Fermi pocket centered away from the towards the zone center
which may coexist with the Fermi arcs. This is discussed in comparison with the
experimental observations.Comment: Some comments and references were added and typos were corrected. The
published version. 9 page
Interplay between spin density wave and phase shifted superconductivity in the Fe pnictide superconductors
We explore if the phase separation or coexistence of the spin density wave
(SDW) and superconductivity (SC) states has any relation to the
incommensurability of the SDW in the Fe pnictide superconductors. A systematic
method of determining the phase separation or coexistence was employed by
computing the anisotropy coefficient from the the 4th order terms of
the Ginzburg--Landau (GL) expansion of the free energy close to the
tricritical/tetracritical point. It was complemented by the self-consistent
numerical iterations of the gap equations to map out the boundaries between the
phase separation and coexistence of the SDW and SC phases, and between
commensurate (C) and incommensurate (IC) SDW in the temperature--doping plane.
Our principal results for the sign reversed -wave pairing SC, in terms of
the multicritical temperature, , the phase separation/coexistence boundary
between the SDW and SC, , and the boundary between C/IC SDW, , are:
(a) IC-SDW and SC coexist for and phase separate otherwise, (b) SDW
takes the C form for and IC form for , and (c) the
thermodynamic first order phase transition intervenes in between the C-SDW and
IC-SDW boundary for large , where is the SDW transition
temperature at zero doping, and . The
intervention makes the phase diagram more complicated than previously reported.
By contrast no coexistence was found for the equal sign pairing SC. These
results will be compared with the experimental reports in the Fe pnictide
superconductors.Comment: 9 pages, 4 figures, Submitted to Phys.Rev.
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