Showing papers by "Matthias Troyer published in 1994"

Thermodynamics and spin gap of the Heisenberg ladder calculated by the look-ahead Lanczos algorithm.

Abstract: We have developed an improved version of the quantum transfer-matrix algorithm. The extreme eigenvalues and eigenvectors of the transfer matrix are calculated by the recently developed look-ahead Lanczos algorithm for non-Hermitian matrices with higher efficiency and accuracy than by the power method. We have applied this method to the antiferromagnetic Heisenberg ladder. The temperature dependence of the susceptibility, specific heat, correlation length, and nuclear spin relaxation rate 1/${\mathit{T}}_{1}$ are calculated. Our results support the existence of a spin gap of about 0.5J.

Pairing and excitation spectrum in doped t-J ladders.

Abstract: Exact-diagonalization studies for a doped t-J ladder (or double chain) show hole pairing in the ground state. The excitation spectrum separates into a limited number of quasiparticles which carry charge +\ensuremath{\Vert}e\ensuremath{\Vert} and spin 1/2 and a triplet mode. At half-filling the former vanish but the latter evolves continuously into the triplet band of the spin liquid. At low doping the quasiparticles form a dilute Fermi gas with a strong attraction but simultaneously the Fermi wave vector, as would be measured in photoemission, is large.