36 research outputs found

### Fusion of the $q$-Vertex Operators and its Application to Solvable Vertex Models

We diagonalize the transfer matrix of the inhomogeneous vertex models of the
6-vertex type in the anti-ferroelectric regime intoducing new types of q-vertex
operators. The special cases of those models were used to diagonalize the s-d
exchange model\cite{W,A,FW1}. New vertex operators are constructed from the
level one vertex operators by the fusion procedure and have the description by
bosons. In order to clarify the particle structure we estabish new isomorphisms
of crystals. The results are very simple and figure out representation
theoretically the ground state degenerations.Comment: 35 page

### Anderson-Yuval approach to the multichannel Kondo problem

We analyze the structure of the perturbation expansion of the general
multichannel Kondo model with channel anisotropic exchange couplings and in the
presence of an external magnetic field, generalizing to this case the
Anderson-Yuval technique. For two channels, we are able to map the Kondo model
onto a generalized resonant level model. Limiting cases in which the equivalent
resonant level model is solvable are identified. The solution correctly
captures the properties of the two channel Kondo model, and also allows an
analytic description of the cross-over from the non Fermi liquid to the Fermi
liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques

### Ground state energy and quasiparticle gaps in $\nu={N\over{2N\pm 1}}$ FQHE states

Applying the transformation of fermion operators to new fermion
quasiparticles introduced by Halperin, Lee, and Read we estimate a scaling
behavior of the ground state energy and quasiparticle gaps as a function of
filling fraction for a "principal sequence" of FQHE $\nu={N\over{2N\pm 1}}$
states converging towards the gapless state at half filling. The exponent
describing the shape of the cusp $\delta E(\nu)\sim |\delta\nu|^{\eta}$ is
found to be greater than one and to depend nontrivially on the interaction
potential. The dependence of quasiparticle gaps agrees with the results of
recent measurements by R.R.Du et al.Comment: 15 pages, TeX, C Version 3.0, preprint ETH-TH/93-3

### Oscillations of the magnetic polarization in a Kondo impurity at finite magnetic fields

The electronic properties of a Kondo impurity are investigated in a magnetic
field using linear response theory. The distribution of electrical charge and
magnetic polarization are calculated in real space. The (small) magnetic field
does not change the charge distribution. However, it unmasks the Kondo cloud.
The (equal) weight of the d-electron components with their magnetic moment up
and down is shifted and the compensating s-electron clouds don't cancel any
longer (a requirement for an experimental detection of the Kondo cloud). In
addition to the net magnetic polarization of the conduction electrons an
oscillating magnetic polarization with a period of half the Fermi wave length
is observed. However, this oscillating magnetic polarization does not show the
long range behavior of Rudermann-Kittel-Kasuya-Yosida oscillations because the
oscillations don't extend beyond the Kondo radius. They represent an internal
electronic structure of the Kondo impurity in a magnetic field. PACS: 75.20.Hr,
71.23.An, 71.27.+

### High $T_c$ Superconductivity, Skyrmions and the Berry Phase

It is here pointed out that the antiferromagnetic spin fluctuation may be
associated with a gauge field which gives rise to the antiferromagnetic ground
state chirality. This is associated with the chiral anomaly and Berry phase
when we consider the two dimensional spin system on the surface of a 3D sphere
with a monopole at the centre. This realizes the RVB state where spinons and
holons can be understood as chargeless spins and spinless holes attached with
magnetic flux. The attachment of the magnetic flux of the charge carrier
suggest, that this may be viewed as a skyrmion. The interaction of a massless
fermion representing a neutral spin with a gauge field along with the
interaction of a spinless hole with the gauge field enhances the
antiferromagnetic correlation along with the pseudogap at the underdoped
region. As the doping increases the antiferromagnetic long range order
disappears for the critical doping parameter $\delta_{sc}$. In this framework,
the superconducting pairing may be viewed as caused by skyrmion-skyrmion bound
states.Comment: 10 pages, accepted in Phys. Rev.

### Determinant Representations of Correlation Functions for the Supersymmetric t-J Model

Working in the $F$-basis provided by the factorizing $F$-matrix, the scalar
products of Bethe states for the supersymmetric t-J model are represented by
determinants. By means of these results, we obtain determinant representations
of correlation functions for the model.Comment: Latex File, 41 pages, no figure; V2: minor typos corrected, V3: This
version will appear in Commun. Math. Phy

### Spin Ordering and Quasiparticles in Spin Triplet Superconducting Liquids

Spin ordering and its effect on low energy quasiparticles in a p-wave
superconducting liquid are investigated. We show that there is a new 2D p-wave
superconducting liquid where the ground state is rotation invariant. In quantum
spin disordered liquids, the low energy quasiparticles are bound states of the
bare Bogolubov- De Gennes ({\em BdeG}) quasiparticles and zero energy
skyrmions, which are charge neutral bosons at the low energy limit. Further
more, spin collective excitations are fractionalized ones carrying a half spin
and obeying fermionic statistics. In thermally spin disordered limits, the
quasi-particles are bound states of bare {\em BdeG} quasi-particles. The
latter situation can be realized in some layered p-wave superconductors where
the spin-orbit coupling is weak.Comment: 5 pages, no figures; published versio

### On magnetic catalysis in even-flavor QED3

In this paper, we discuss the role of an external magnetic field on the
dynamically generated fermion mass in even-flavor QED in three space-time
dimensions. Based on some reasonable approximations, we present analytic
arguments on the fact that, for weak fields, the magnetically-induced mass
increases quadratically with increasing field, while at strong fields one
crosses over to a mass scaling logarithmically with the external field. We also
confirm this type of scaling behavior through quenched lattice calculations
using the non-compact version for the gauge field. Both the zero and finite
temperature cases are examined. A preliminary study of the fermion condensate
in the presence of magnetic flux tubes on the lattice is also included.Comment: 38 pages latex, 18 figures and a style file (axodraw) incorporated
(some clarifying remarks concerning the validity of the approximations made
and some references were added correcting an earlier version; no effect on
conclusions; version to appear in Phys. Rev. D.

### A Coulomb gas approach to the anisotropic one-dimensional Kondo lattice model at arbitrary filling

We establish a mapping of a general spin-fermion system in one dimension into
a classical generalized Coulomb gas. This mapping allows a renormalization
group treatment of the anisotropic Kondo chain both at and away from
half-filling. We find that the phase diagram contains regions of paramagnetism,
partial and full ferromagnetic order. We also use the method to analyze the
phases of the Ising-Kondo chain.Comment: 19 pages, 9 figure

### Application of the Density Matrix Renormalization Group in momentum space

We investigate the application of the Density Matrix Renormalization Group
(DMRG) to the Hubbard model in momentum-space. We treat the one-dimensional
models with dispersion relations corresponding to nearest-neighbor hopping and
$1/r$ hopping and the two-dimensional model with isotropic nearest-neighbor
hopping. By comparing with the exact solutions for both one-dimensional models
and with exact diagonalization in two dimensions, we first investigate the
convergence of the ground-state energy. We find variational convergence of the
energy with the number of states kept for all models and parameter sets. In
contrast to the real-space algorithm, the accuracy becomes rapidly worse with
increasing interaction and is not significantly better at half filling. We
compare the results for different dispersion relations at fixed interaction
strength over bandwidth and find that extending the range of the hopping in one
dimension has little effect, but that changing the dimensionality from one to
two leads to lower accuracy at weak to moderate interaction strength. In the
one-dimensional models at half-filling, we also investigate the behavior of the
single-particle gap, the dispersion of spinon excitations, and the momentum
distribution function. For the single-particle gap, we find that proper
extrapolation in the number of states kept is important. For the spinon
dispersion, we find that good agreement with the exact forms can be achieved at
weak coupling if the large momentum-dependent finite-size effects are taken
into account for nearest-neighbor hopping. For the momentum distribution, we
compare with various weak-coupling and strong-coupling approximations and
discuss the importance of finite-size effects as well as the accuracy of the
DMRG.Comment: 15 pages, 11 eps figures, revtex