Excitation spectrum and ground state properties of the S=1/2 Heisenberg ladder with staggered dimerization

TL;DR

This study investigates the excitation spectrum and phase transitions of a spin-1/2 Heisenberg ladder with staggered dimerization using series expansions, diagrammatic analysis, and exact diagonalization, revealing two massive phases and a critical transition.

Contribution

It introduces a comprehensive analysis combining multiple methods to characterize phase boundaries and excitation spectra in a staggered dimerized spin ladder.

Findings

Identification of two massive phases with different correlations

Detection of a phase transition characterized by triplet spectrum softening

Determination of the phase boundary location

Abstract

We have studied the excitation spectrum of the $S=1/2$ quantum spin ladder with staggered dimerization by dimer series expansions, diagrammatic analysis of an effective interacting Bose gas of local triplets, and exact diagonalization of small clusters. We find that the model has two massive phases, with predominant inter-chain (rung) or intra-chain correlations. The transition from the rung dimer into the intra-chain dimer phase is characterized by softening of the triplet spectrum at $k=\pi$. The excitation spectrum as well as the spin correlations away from and close to the critical line are calculated. The location of the phase boundary is also determined.