1,059 research outputs found
Superconductivity and Spin Fluctuations
The organizers of the Memorial Session for Herman Rietschel asked that I
review some of the history of the interplay of superconductivity and spin
fluctuations. Initially, Berk and Schrieffer showed how paramagnon spin
fluctuations could suppress superconductivity in nearly-ferromagnetic
materials. Following this, Rietschel and various co-workers wrote a number of
papers in which they investigated the role of spin fluctuations in reducing the
T_c of various electron-phonon superconductors. Paramagnon spin fluctuations
are also believed to provide the p-wave pairing mechanism responsible for the
superfluid phases of . More recently, antiferromagnetic spin fluctuations
have been proposed as the mechanism for d-wave pairing in the heavy-fermion
superconductors and in some organic materials as well as possibly the high T_c
cuprates. Here I will review some of this early history and discuss some of the
things we have learned more recently from numerical simulations.Comment: 9 pages, 10 encapsulated figures, Presented at MOS99, International
Conference on Physics and Chemistry of Molecular and Oxide Superconductors,
Stockholm, Sweden, 28 July-2 Aug, 1999, corrected typo
Determining the structure of the superconducting gap in Cu_{2}O_{3} 2-leg ladder materials
Superconductivity has been recently observed in
Sr_{0.4}Ca_{13.6}Cu_{24}O_{41.84} which contains quasi-one-dimensional
Cu_{2}O_{3} 2-leg ladders. If, as suggested by some theories, the
superconductivity arises from these 2-leg ladders, it will be important to
determine the structure of the superconducting gap. In particular, does the gap
in a 2-leg ladder change sign when one goes from the bonding to antibonding
fermi surface points? Here we carry out phenomenological calculations of
nuclear relaxation rates and inelastic neutron scattering intensity in order to
provide estimates of the experimental resolution that will be required to
determine the structure of the superconducting gap associated with an array of
weakly coupled 2-leg ladders.Comment: 12 pages including 7 eps figures, uses revtex with eps
Spin Susceptibility Representation of the Pairing Interaction for the two-dimensional Hubbard Model
Using numerical dynamic cluster quantum Monte Carlo results, we study a
simple approximation for the pairing interaction of a two-dimensional Hubbard
model with an on-site Coulomb interaction equal to the bandwidth. We find
that with an effective temperature dependent coupling \Ub(T) and the
numerically calculated spin susceptibility , the d-wave pairing
interaction is well approximated by \frac{3}{2} \Ub^2\chi(K-K').Comment: 5 pages, 7 figure
Fermi-liquid based theory for the in-plane magnetic anisotropy in untwinned high-T superconductors
Using a generalized RPA-type theory we calculate the in-plane anisotropy of
the magnetic excitations in hole-doped high- superconductors. Extending
our earlier Fermi-liquid based studies on the resonance peak by inclusion of
orthorhombicity we still find two-dimensional spin excitations, however, being
strongly anisotropic. This reflects the underlying anisotropy of the hopping
matrix elements and of the resultant superconducting gap function. We compare
our calculations with new experimental data on {\it fully untwinned}
and find good agreement. Our results are in contrast
to earlier interpretations on the in-plane anisotropy in terms of stripes (H.
Mook {\it et al.}, Nature {\bf 404}, 729 (2000)), but reveal a conventional
solution to this important problem.Comment: 5 pages, 6 figure
Neutron scattering as a probe of the Fe-pnicitide superconducting gap
Inelastic neutron scattering provides a probe for studying the spin and
momentum structure of the superconducting gap. Here, using a two-orbital model
for the Fe-pnicitide superconductors and an RPA-BCS approximation for the
dynamic spin susceptibility, we explore the scattering response for various
gaps that have been proposed.Comment: 5 pages, 4 figure
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