75 research outputs found
Spectral properties of the one-dimensional two-channel Kondo lattice model
We have studied the energy spectrum of a one-dimensional Kondo lattice, where
the localized magnetic moments have SU(N) symmetry and two channels of
conduction electrons are present. At half filling, the system is shown to exist
in two phases: one dominated by RKKY-exchange interaction effects, and the
other by Kondo screening. A quantum phase transition point separates these two
regimes at temperature . The Kondo-dominated phase is shown to possess
soft modes, with spectral gaps much smaller than the Kondo temperature.Comment: 4 pages + 2 figures. Submitted for publicatio
Analytical results for the Coqblin-Schrieffer model with generalized magnetic fields
Using the approach alternative to the traditional Thermodynamic Bethe Ansatz,
we derive analytical expressions for the free energy of Coqblin-Schrieffer
model with arbitrary magnetic and crystal fields. In Appendix we discuss two
concrete examples including the field generated crossover from the SU(4) to the
SU(2) symmetry in the SU(4)-symmetric model.Comment: 5 page
A Model with Propagating Spinons beyond One Dimension
For the model of frustrated spin-1/2 Heisenberg magnet described in A. A.
Nersesyan and A. M. Tsvelik, (Phys. Rev. B{\bf 67}, 024422 (2003)) we calculate
correlation functions of staggered magnetization and dimerization. The model is
formulated as a collection of antiferromagnetic chains weakly coupled by a
frustrated exchange interaction. The calculation done for the case of four
chains demonstrates that these functions do not vanish. Since the correlation
functions in question factorize into a product of correlation functions of
spinon creation and annihilation operators, this constitutes a proof that
spinons in this model propagate in the direction perpendicular to the chains.Comment: revised version to appear in Phys. Rev B., 8 pages, a reference adde
Doping of a Spin-1 Chain: An Integrable Model
An exactly soluble model describing a spin S=1 antiferromagnetic chain doped with mobile S=1/2 carriers is constructed. In its continuum limit the undoped state is described by three gapless Majorana fermions composing the SU(2) triplet. Doping adds a scalar charge field and a singlet Majorana fermion with different velocity. We argue that this mode survives when the Haldane gap is added
A Mechanism for Ferrimagnetism and Incommensurability in One-Dimensional Systems
A mechanism for ferrimagnetism in
(1+1)-dimensions is discussed. The ferrimagnetism is cased by interactions
described by operators with non-zero conformal spin. Such interactions appear
in such problems as the problem of tunneling between Luttinger liquids and the
problem of frustrated spin ladder. I present exact solutions for a
representative class of models containing such interactions together with a
simple mean field analysis. It is shown that the interactions (i) dynamically
generate static oscillations with a wave vector dependent on the coupling
constant, (ii) give rise to a finite magnetic moment at accompanied by
the soft mode with a non-relativistic ({\it ferromagnetic}) dispersion , (iii) generate massive (roton) modes.Comment: replaced by the extended version, references adde
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
Kink Confinement and Supersymmetry
We analyze non-integrable deformations of two-dimensional N=1 supersymmetric
quantum field theories with kink excitations. As example, we consider the
multi-frequency Super Sine Gordon model. At weak coupling, this model is robust
with respect to kink confinement phenomena, in contrast to the purely bosonic
case. If we vary the coupling, the model presents a sequence of phase
transitions, where pairs of kinks disappear from the spectrum. The phase
transitions fall into two classes: the first presents the critical behaviors of
the Tricritical Ising model, the second instead those of the gaussian model. In
the first case, close to the critical point, the model has metastable vacua,
with a spontaneously supersymmetry breaking. When the life-time of the
metastable vacua is sufficiently long, the role of goldstino is given by the
massless Majorana fermion of the Ising model. On the contrary, supersymmetry
remains exact in the phase transition of the second type.Comment: 29 pages, 12 figure
Logarithmic Operators and Dynamical Extention of The Symmetry Group in the Bosonic SU(2)_0 and SUSY SU(2)_2 WZNW Models
We study the operator product expansion in the bosonic and SUSY
WZNW models. We find that these OPEs contain both logarithmic
operators and new conserved currents, leading to an extension of the symmetry
group.Comment: 16 pages, Late
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