1,953 research outputs found
Attenuated total reflection enhanced photoejection from cathodes Final report
Optical equations governing interaction between radiation and interface of two media using metallic cathode
Disorder effect in low dimensional superconductors
The quasiparticle density of states (DOS), the energy gap, the superfluid
density , and the localization effect in the s- and d-wave
superconductors with non-magnetic impurity in two dimensions (2D) are studied
numerically. For strong (unitary) scatters, we find that it is the range of the
scattering potential rather than the symmetry of the superconducting pairing
which is more important in explaining the impurity dependences of the specific
heat and the superconducting transition temperature in Zn doped YBCO. The
localization length is longer in the d-wave superconducting state than in the
normal state, even in the vicinity of the Fermi energy.Comment: 2 pages, uuencoded compressed postscript file, IRC-940610
Evolution of the neutron resonances in AFe2Se2
Recent experiments on the alkali-intercalated iron selenides have raised
questions about the symmetry of the superconducting phase. Random phase
approximation calculations of the leading pairing eigenstate for a tight-
binding 5-orbital Hubbard-Hund model of AFe2Se2 find that a d-wave (B1g) state
evolves into an extended s{\pm} (A1g) state as the system is hole-doped.
However, over a range of doping these two states are nearly degenerate. Here,
we calculate the imaginary part of the magnetic spin susceptibility
\chi"(q,{\omega}) for these gaps and discuss how the evolution of neutron
scattering resonances can distinguish between them
Raising the critical temperature by disorder in unconventional superconductors mediated by spin fluctuations
We propose a mechanism whereby disorder can enhance the transition
temperature Tc of an unconventional superconductor with pairing driven by
exchange of spin fluctuations. The theory is based on a self-consistent real
space treatment of pairing in the disordered one-band Hubbard model. It has
been demonstrated before that impurities can enhance pairing by softening the
spin fluctuations locally; here, we consider the competing effect of
pair-breaking by the screened Coulomb potential also present. We show that,
depending on the impurity potential strength and proximity to magnetic order,
this mechanism results in a weakening of the disorder-dependent Tc-suppression
rate expected from Abrikosov-Gor'kov theory, or even in disorder-generated Tc
enhancements.Comment: 6 pages, 4 figures + Supplementary Materia
Universal zero-frequency Raman slope in a d-wave superconductor
It is known that for an unconventional superconductor with nodes in the gap,
the in-plane microwave or dc conductivity saturates at low temperatures to a
universal value independent of the impurity concentration. We demonstrate that
a similar feature can be accessed using channel-dependent Raman scattering. It
is found that, for a -wave superconductor, the slope of
low-temperature Raman intensity at zero frequency is universal in the
and channels, but not in the channel. Moreover, as opposed to
the microwave conductivity, universal Raman slopes are sensitive not only to
the existence of a node, but also to different pairing states and should allow
one to distinguish between such pairing states.Comment: 5 page
Origin of Gap Anisotropy in Spin Fluctuation Models of the Fe-pnictides
We discuss the large gap anisotropy found for the A1g (s-wave) state in RPA
spin-fluctuation and functional renormalization group calculations and show how
the simple arguments leading to isotropic sign-switched s-wave states in these
systems need to be supplemented by a consideration of pair scattering within
Fermi surface sheets and between the individual electron sheets as well. In
addition, accounting for the orbital makeup of the states on the Fermi surface
is found to be crucial.Comment: 6 pages, 7 figure
Local modulations of the spin-fluctuation mediated pairing interaction by impurities in d-wave superconductors
We present a self-consistent real space formulation of spin-fluctuation
mediated d-wave pairing. By calculating all relevant inhomogeneous spin and
charge susceptibilities in real space within the random phase approximation
(RPA), we obtain the effective pairing interaction and study its spatial
dependence near both local potential and hopping impurities. A remarkably large
enhancement of the pairing interaction may be obtained near the impurity site.
We discuss the relevance of our result to inhomogeneities observed by scanning
tunneling spectroscopy on the surface of cuprate superconductors.Comment: 8 pages, 7 figure
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