76 research outputs found
Non-k-diagonality in the interlayer pair-tunneling model of high-temperature superconductivity
We investigate the effect of k-space broadening of the interlayer pairing
kernel on the critical temperature T_c and the k-dependence of the gap function
in a one-dimensional version of the interlayer pair-tunneling model of high-T_c
superconductivity. We consider constant as well as k-dependent intralayer
pairing kernels. We find that the sensitivity to k-space broadening is larger
the smaller the width of the peak of the Fermi-level gap calculated for zero
broadening. This width increases with the overall magnitude of the interlayer
tunneling matrix element, and decreases with the bandwidth of the
single-electron intralayer excitation spectrum. The width also increases as the
Fermi level is moved towards regions where the excitation spectrum flattens
out. We argue that our qualitative conclusions are valid also for a
two-dimensional model. This indicates that at or close to half-filling in two
dimensions, when the Fermi-surface gap for zero broadening attains its peaks at
and where the excitation spectrum is flat, these
peaks should be fairly robust to moderate momentum broadening.Comment: 10 pages including 4 figures, to be published in Journal of Low
Temperature Physic
Critical properties of the N-color London model
The critical properties of -color London model are studied in
dimensions. The model is dualized to a theory of vortex fields interacting
through a Coulomb and a screened potential. The model with N=2 shows two
anomalies in the specific heat. From the critical exponents and ,
the mass of the gauge field, and the vortex correlation functions, we conclude
that one anomaly corresponds to an {\it inverted} \xy fixed point, while the
other corresponds to a \xy fixed point. There are fixed points, namely one
corresponding to an inverted \xy fixed point, and corresponding to
neutral \xy fixed points. This represents a novel type of quantum fluid, where
superfluid modes arise out of charged condensates.Comment: 4 pages, 3 figures, new references added. Accepted for publication in
Physical Review Letter
Phase structure of Abelian Chern-Simons gauge theories
We study the effect of a Chern-Simons (CS) term in the phase structure of two
different Abelian gauge theories. For the compact Maxwell-Chern-Simons theory,
we obtain that for values of the CS coupling with ,
the theory is equivalent to a gas of closed loops with contact interaction,
exhibiting a phase transition in the universality class. We also employ
Monte Carlo simulations to study the noncompact U(1) Abelian Higgs model with a
CS term. Finite size scaling of the third moment of the action yields critical
exponents and that vary continuously with the strength of the CS
term, and a comparison with available analytical results is made.Comment: RevTex4, 4 pages, 1 figure; v3: improvements and corrections made in
the first part of the paper; references added. To be published in Europhysics
Letter
Compact U(1) gauge theories in 2+1 dimensions and the physics of low dimensional insulating materials
Compact abelian gauge theories in dimensions arise often as an
effective field-theoretic description of models of quantum insulators. In this
paper we review some recent results about the compact abelian Higgs model in
in that context.Comment: 5 pages, 3 figures; based on talk by F.S. Nogueira in the Aachen
HEP2003 conferenc
Pairing Symmetry Conversion by Spin-Active Interfaces in Magnetic Normal-Metal-Superconductor Junctions
Polarization Selection Rules and Superconducting Gap Anisotropy in
We discuss polarization selection rules for angle-resolved photoemission
spectroscopy in Bi2212. Using these we show that the ``hump'' in the
superconducting gap observed in the quadrant in our earlier work is not on
the main band, but rather on an umklapp band arising from the
structural superlattice. The intrinsic gap is most likely quite small over a
range of about the diagonal directions.Comment: 3 pages, revtex, 3 uuencoded postscript figure
Ginzburg-Landau Expansion in Non-Fermi Liquid Superconductors: Effect of the Mass Renormalization Factor
We reconsider the Ginzburg-Landau expansion for the case of a non-Fermi
liquid superconductor. We obtain analytical results for the Ginzburg-Landau
functional in the critical region around the superconducting phase transition,
T <= T_c, in two special limits of the model, i.e., the spin-charge separation
case and the anomalous Fermi liquid case. For both cases, in the presence of a
mass renormalization factor, we derived the form and the specific dependence of
the coherence length, penetration depth, specific heat jump at the critical
point, and the magnetic upper critical field. For both limits the obtained
results reduce to the usual BCS results for a two dimensional s-wave
superconductor. We compare our results with recent and relevant theoretical
work. The results for a d--wave symmetry order parameter do not change
qualitatively the results presented in this paper. Only numerical factors
appear additionally in our expressions.Comment: accepted for publication in Physical Review
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