arXiv subjects

A. Parola

Publications and source records attributed to A. Parola.

40 records · Page 3Linked to original sources

arXiv1996

Spectral properties of one dimensional insulators and superconductors

Conformal field theory and Bethe ansatz are used to investigate the low energy features of the spectral function in one dimensional models which exhibit a gap in the spin or in the charge excitation spectrum. Exotic behavior is found in the superconducting case, where the Green function displays momentum dependent Luttinger Liquid exponents. The predictions of the formalism are confirmed by Lanczos diagonalizations in the $tJ$ model up to 32 sites. These results may be relevant in connection to photoemission experiments in quasi one dimensional insulators or superconductors.

cond-mat↗

arXiv1993

Hole dynamics in a quantum antiferromagnet beyond the retraceable path approximation

The one-hole spectral weight for two chains and two dimensional lattices is studied numerically using a new method of analysis of the spectral function within the Lanczos iteration scheme: the Lanczos spectra decoding method. This technique is applied to the $t-J_z$ model for $J_z \to 0$, directly in the infinite size lattice. By a careful investigation of the first 13 Lanczos steps and the first 26 ones for the two dimensional and the two chain cases respectively, we get several new features of the one-hole spectral weight. A sharp incoherent peak with a clear momentum dispersion is identified, together with a second broad peak at higher energy. The spectral weight is finite up to the Nagaoka energy where it vanishes in a non-analytic way. Thus the lowest energy of one hole in a quantum antiferromagnet is degenerate with the Nagaoka energy in the thermodynamic limit.

cond-mat↗

arXiv1993

Realization of a Spin liquid in a Two Dimensional Quantum Antiferromagnet

The ground state properties of the two dimensional spatially anisotropic Heisenberg model are investigated by use of field theory mappings, spin-wave expansion and Lanczos technique. Evidence for a disorder transition induced by anisotropy at about $J_y/J_x < 0.1$ is shown. We argue that the disordered phase is gapless and its long wavelength properties can be interpreted in terms of decoupled one dimensional chains.

cond-mat↗

arXiv1992

Spin-Charge separation in a model of two coupled chains

A model of interacting electrons living on two chains coupled by a transverse hopping $t_\perp$, is solved exactly by bosonization technique. It is shown that $t_\perp$ does modify the shape of the Fermi surface also in presence of interaction, although charge and spin excitations keep different velocities $u_ρ$, $u_σ$. Two different regimes occur: at short distances, $x\ll ξ= (u_ρ- u_σ)/4t_\perp$, the two chain model is not sensitive to $t_\perp$, while for larger separation $x\gg ξ$ inter--chain hopping is relevant and generates further singularities in the electron Green function besides those due to spin-charge decoupling. (2 figures not included. Figure requests: FABRIZIO@ITSSISSA)

cond-mat↗