Light induced magnetization in a spin S=1 easy-plane antiferromagnetic chain

The time evolution of magnetization induced by circularly polarized light in a $S=1$ Heisenberg chain with large, easy--plane anisotropy is studied numerically and analytically. Results at constant light frequency $\Omega=\Omega_0$ are interpreted in terms of absorption lines of the electronic spin resonance spectrum. Applying a time dependent light frequency $\Omega=\Omega(t)$, so called chirping, is shown to be an efficient procedure in order to obtain within a short time a large, controlled value of the magnetization $M^z$. Furthermore, comparison with a $2$ - level model provides a qualitative understanding of the induced magnetization process

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

Anomalous scaling of conductivity in integrable fermion systems

We analyze the high-temperature conductivity in one-dimensional integrable models of interacting fermions: the t-V model (anisotropic Heisenberg spin chain) and the Hubbard model, at half-filling in the regime corresponding to insulating ground state. A microcanonical Lanczos method study for finite size systems reveals anomalously large finite-size effects at low frequencies while a frequency-moment analysis indicates a finite d.c. conductivity. This phenomenon also appears in a prototype integrable quantum system of impenetrable particles, representing a strong-coupling limit of both models. In the thermodynamic limit, the two results could converge to a finite d.c. conductivity rather than an ideal conductor or insulator scenario.Comment: 6 pages, 3 figures. Submitted to PR

Domain wall dynamics in integrable and chaotic spin-1/2 chains

We study the time evolution of correlation functions, spin current, and local magnetization in an isolated spin-1/2 chain initially prepared in a sharp domain wall state. The results are compared with the level of spatial delocalization of the eigenstates of the system which is measured using the inverse participation ratio. Both integrable and non-integrable regimes are considered. Non-integrability is introduced to the integrable Hamiltonian with nearest neighbor couplings by adding a single site impurity field or by adding next-nearest-neighbor couplings. A monotonic correspondence between the enhancement of the level of delocalization, spin current and magnetization dynamics occurs in the integrable domain. This correspondence is however lost for chaotic models with weak Ising interactions.Comment: 9 pages, 5 figures, 1 tabl

Integrability and ideal conductance at finite temperatures

We analyse the finite temperature charge stiffness D(T>0), by a generalization of Kohn's method, for the problem of a particle interacting with a fermionic bath in one dimension. We present analytical evidence, using the Bethe ansatz method, that D(T>0) is finite in the integrable case where the mass of the particle equals the mass of the fermions and numerical evidence that it vanishes in the nonintegrable one of unequal masses. We conjecture that a finite D(T>0) is a generic property of integrable systems.Comment: revtex file; 3 postscript figure files replaced with uuencoded one

On the nonlinear response of a particle interacting with fermions in a 1D lattice

By the Bethe ansatz method we study the energy dispersion of a particle interacting by a local interaction with fermions (or hard core bosons) of equal mass in a one dimensional lattice. We focus on the period of the Bloch oscillations which turns out to be related to the Fermi wavevector of the Fermi sea and in particular on how this dispersion emerges as a collective effect in the thermodynamic limit. We show by symmetry that the dispersion is temperature independent for a half-filled system. We also discuss the adiabatic coherent collective response of the particle to an applied field.Comment: 4 pages, 4 figure

Transport properties of a spin-1/2 Heisenberg chain with an embedded spin-S impurity

The finite temperature transport properties of a spin-1/2 anisotropic Heisenberg chain with an embedded spin-S impurity are studied. Using primarily numerical diagonalization techniques, we study the dependence of the dynamical spin and thermal conductivities on the lattice size, the magnitude of the impurity spin, the host-impurity coupling, the easy axis anisotropy, as well as the dependence on temperature. Particularly for the temperature dependence, we discuss the screening of the impurity by the chain eventually leading to the cutting or healing of the host chain. Numerical results are supported by analytical arguments obtained in the strong host-impurity coupling regime.Comment: 7 pages, 10 figure