Studies of Quantum Spin Ladders at T=0 and at High Temperatures by Series Expansions

TL;DR

This paper uses series expansion methods to analyze quantum spin ladders at zero and high temperatures, confirming a gap in 2-chain systems and a gapless spectrum in 3-chain systems, with detailed thermodynamic property calculations.

Contribution

It provides comprehensive series expansion results for 2- and 3-chain spin-half ladders, including dispersion relations and thermodynamic properties, clarifying their spectral and magnetic behaviors.

Findings

2-chain ladders have a persistent energy gap for all non-zero interchain couplings.

3-chain ladders exhibit a gapless spectrum.

Susceptibility approaches zero for 2-chain and a finite value for 3-chain as T approaches zero.

Abstract

We have carried out extensive series studies, at T=0 and at high temperatures, of 2-chain and 3-chain spin-half ladder systems with antiferromagnetic intrachain and both antiferromagnetic and ferromagnetic interchain couplings. Our results confirm the existence of a gap in the 2-chain Heisenberg ladders for all non-zero values of the interchain couplings. Complete dispersion relations for the spin-wave excitations are computed. For 3-chain systems, our results are consistent with a gapless spectrum. We also calculate the uniform magnetic susceptibility and specific heat as a function of temperature. We find that as $T\to 0$, for the 2-chain system the uniform susceptibility goes rapidly to zero, whereas for the 3-chain system it approaches a finite value. These results are compared in detail with previous studies of finite systems.