Incommensuration in quantum antiferromagnetic chain

TL;DR

This paper investigates how weak incommensurate modulations in a dimerized quantum antiferromagnetic chain induce a quantum critical point and transition to a gapless state, revealing universality with classical transitions.

Contribution

It demonstrates that incommensurate modulations cause a quantum phase transition in dimerized chains, connecting quantum criticality with classical commensurate-incommensurate transitions.

Findings

Incommensurate modulation induces a quantum critical point.

Transition to a gapless state occurs as wavelength varies.

Critical behavior matches the Pokrovsky-Talapov universality class.

Abstract

A dimerized quantum Heisenberg or XY antiferromagnetic chain has a gap in the spectrum. We show that a weak incommensurate modulation around a dimerized chain produces a zero temperature quantum critical point. As the incommensuration wavelength is varied, there is a transition to a modulated gapless state. The critical behaviour is in the universality class of the classical commensurate-incommensurate (Pokrovsky-Talapov) transition. An analogous metal-insulator transition can also take place for an incommensurate chain.