698 research outputs found
Interaction induced dimerization in zigzag single wall carbon nanotubes
We derive a low-energy effective model of metallic zigzag carbon nanotubes at
half filling. We show that there are three important features characterizing
the low-energy properties of these systems: the long-range Coulomb interaction,
umklapp scattering and an explicit dimerization generated by interactions. The
ratio of the dimerization induced gap and the Mott gap induced by the umklapp
interactions is dependent on the radius of the nanotube and can drive the
system through a quantum phase transition with SU(2)_1 quantum symmetry. We
consider the physical properties of the phases on either side of this
transition which should be relevant for realistic nanotubes.Comment: 8 pages, 5 figure
Crystal Distortion and the Two-Channel Kondo Effect
We study a simple model of the two-channel Kondo effect in a distorted
crystal. This model is then used to investigate the interplay of the Kondo and
Jahn-Teller effects, and also the Kondo effect in an impure crystal. We find
that the Jahn-Teller interaction modifies the characteristic energy scale of
the system below which non-Fermi-liquid properties of the model become
apparent. The modified energy scale tends to zero as the limit of a purely
static Jahn-Teller effect is approached. We find also that the non-Fermi-liquid
properties of the quadrupolar Kondo effect are not stable against crystal
distortion caused by impurities.Comment: 11 page
Comment on ``Enhancement of the Tunneling Density of States in Tomonaga-Luttinger Liquids''
In a recent Physical Review Letter, Oreg and Finkel'stein (OF) have
calculated the electron density of states (DOS) for tunneling into a repulsive
Luttinger liquid close to the location of an impurity. The result of their
calculation is a DOS which is enhanced with respect to the pure system, and
moreover diverging for not too strong repulsion. In this Comment we intend to
show that OF's calculation suffers from a subtle flaw which, being corrected,
results into a DOS not only vanishing at zero frequency but in fact suppressed
in comparison with the DOS of a pure Luttinger liquid.Comment: 1 page, Revte
Dimerized phase and transitions in a spatially anisotropic square lattice antiferromagnet
We investigate the spatially anisotropic square lattice quantum
antiferromagnet. The model describes isotropic spin-1/2 Heisenberg chains
(exchange constant J) coupled antiferromagnetically in the transverse (J_\perp)
and diagonal (J_\times), with respect to the chain, directions. Classically,
the model admits two ordered ground states -- with antiferromagnetic and
ferromagnetic inter-chain spin correlations -- separated by a first order phase
transition at J_\perp=2J_\times. We show that in the quantum model this
transition splits into two, revealing an intermediate quantum-disordered
columnar dimer phase, both in two dimensions and in a simpler two-leg ladder
version. We describe quantum-critical points separating this spontaneously
dimerized phase from classical ones.Comment: 4 pages, 2 figure
Class of exactly soluble models of one-dimensional spinless fermions and its application to the Tomonaga-Luttinger Hamiltonian with nonlinear dispersion
It is shown that for some special values of Hamiltonian parameters the
Tomonaga-Luttinger model with nonlinear dispersion is unitary equivalent to the
system of noninteracting fermions. For such parameter values the
density-density propagator of the Tomonaga-Luttinger Hamiltonian with nonlinear
dispersion can be found exactly. In a generic situation the exact solution can
be used as a reference point around which a perturbative expansion in orders of
certain irrelevant operators may be constructed.Comment: 12 pages, 0 figure, revtex
- …