15 research outputs found
Spin Conductance in one-dimensional Spin-Phonon systems
We present results for the spin conductance of the one dimensional spin-1/2
Heisenberg and XY model coupled to phonons. We apply an approach based on the
Stochastic Series Expansion (Quantum Monte Carlo) method to evaluate the
conductance for a variety of phonon dispersions and values of spin-phonon
coupling. From our numerical simulations and analytical arguments, we derive
several scaling laws for the conductance.Comment: 7 pages, 9 figure
Thermal conductivity of anisotropic spin - 1/2 two leg ladder:Green's function approach
We study the thermal transport of a spin-1/2 two leg antiferromagnetic ladder
in the direction of legs. The possible effect of spin-orbit coupling and
crystalline electric field are investigated in terms of anisotropies in the
Heisenberg interactions on both leg and rung couplings. The original spin
ladder is mapped to a bosonic model via a bond-operator transformation where an
infinite hard-core repulsion is imposed to constrain one boson occupation per
site. The Green's function approach is applied to obtain the energy spectrum of
quasi-particle excitations responsible for thermal transport. The thermal
conductivity is found to be monotonically decreasing with temperature due to
increased scattering among triplet excitations at higher temperatures. A tiny
dependence of thermal transport on the anisotropy in the leg direction at low
temperatures is observed in contrast to the strong one on the anisotropy along
the rung direction, due to the direct effect of the triplet density. Our
results reach asymptotically the ballistic regime of the spin - 1/2 Heisenberg
chain and compare favorably well with exact diagonalization data
Reactive Hall and Edelstein effects in a tight-binding model with spin-orbit coupling
The reactive Hall constant R_H, described by reactive (nondissipative)
conductivities, is analyzed within linear response theory in the presence of
spin-orbit interaction. Within a two dimensional tight-binding model the effect
of van Hove singularities is studied. Along the same line a formulation of the
Edelstein constant is proposed and studied as a function of coupling parameters
and fermion filling.Comment: 7 pages, 5 figure
Quantum Monte Carlo study of the 3D attractive Hubbard model
We study the three-dimensional (3D) attractive Hubbard model by means of the
Determinant Quantum Monte Carlo method. This model is a prototype for the
description of the smooth crossover between BCS superconductivity and
Bose-Einstein condensation. By detailed finite-size scaling we extract the
finite-temperature phase diagram of the model. In particular, we interpret the
observed behavior according to a scenario of two fundamental temperature
scales; T* associated with Cooper pair formation and Tc with condensation
(giving rise to long-range superconducting order). Our results also indicate
the presence of a recently conjectured phase transition hidden by the
superconducting state. A comparison with the 2D case is briefly discussed,
given its relevance for the physics of high-Tc cuprate superconductors.Comment: 4 pages, 4 Postscript figure