Ground State of a Heisenberg Chain with Next-Nearest-Neighbor Bond Alternation

TL;DR

This paper studies the ground state of a frustrated spin chain with bond alternation, revealing a transition from a gapless Luttinger liquid to a dimerized gapped phase, using conformal field theory and exact diagonalizations.

Contribution

It provides a detailed numerical analysis of the phase boundary and the effects of bond alternation on the frustrated Heisenberg chain's ground state.

Findings

Luttinger spin-fluid phase for small frustration

Spontaneous dimerization at high frustration

Bond alternation reduces the triplet gap and shifts the phase boundary

Abstract

We investigate the ground-state properties of the spin-half $J_1{-}J_2$ Heisenberg chain with a next-nearest-neighbor spin-Peierls dimerization using conformal field theory and Lanczos exact diagonalizations. In agreement with the results of a recent bosonization analysis by Sarkar and Sen, we find that for small frustration ($J_2/J_1$) the system is in a Luttinger spin-fluid phase, with gapless excitations, and a finite spin-wave velocity. In the regime of strong frustration the ground state is spontaneously dimerized and the bond alternation reduces the triplet gap, leading to a slight enhancement of the critical point separating the Luttinger phase from the gapped one. An accurate determination of the phase boundary is obtained numerically from the study of the excitation spectrum.