1,863 research outputs found
Quantum phase transition between one-channel and two-channel Kondo polarons
For a mobile spin-1/2 impurity, coupled antiferromagnetically to a
one-dimensional gas of fermions, perturbative ideas have been used to argue in
favor of two-channel Kondo behavior of the impurity spin. Here we combine
general considerations and extensive numerical simulations to show that the
problem displays a novel quantum phase transition between two-channel and
one-channel Kondo screening upon increasing the Kondo coupling. We construct a
ground-state phase diagram and discuss the various non-trivial crossovers as
well as possible experimental realizations.Comment: 5+4 pages, 5+3 fig
Superconductivity with s and p-symmetries in an extended Hubbard model with correlated hopping
We consider a generalized Hubbard model with on-site and nearest-neighbour
repulsions U and V respectively, and nearest-neighbour hopping for spin up
(down) which depends on the total occupation n_b of spin down (up) electrons on
both sites involved. The hopping parameters are t_{AA}, t_{AB} and t_{BB} for
n_b=0,1,2 respectively. We briefly summarize results which support that the
model exhibits s-wave superconductivity for certain parameters and extend them
by studying the Berry phases. Using a generalized Hartree-Fock(HF) BCS
decoupling of the two and three-body terms, we obtain that at half filling, for
t_{AB}<t_{AA}=t_{BB} and sufficiently small U and V the model leads to triplet
p-wave superconductivity for a simple cubic lattice in any dimension. In one
dimension, the resulting phase diagram is compared with that obtained
numerically using two quantized Berry phases (topological numbers) as order
parameters. While this novel method supports the previous results, there are
quantitative differences.Comment: Latex file, 14 pages, 2 postscript figure
Critical behavior of the S=3/2 antiferromagnetic Heisenberg chain
Using the density-matrix renormalization-group technique we study the
long-wavelength properties of the spin S=3/2 nearest-neighbor Heisenberg chain.
We obtain an accurate value for the spin velocity v=3.8+- 0.02, in agreement
with experiment. Our results show conclusively that the model belongs to the
same universality class as the S=1/2 Heisenberg chain, with a conformal central
charge c=1 and critical exponent eta=1Comment: RevTeX (version 3.0), 4 twocolumn pages with 4 embedded figure
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