Exotic gapless spectrum induced by frustration in quantum antiferromagnets

TL;DR

This paper provides numerical evidence for a nearly gapless spectrum with boundary edge states in frustrated spin-1/2 antiferromagnetic ladders, revealing an unconventional spin-liquid phase stabilized by frustration.

Contribution

It introduces a projected BCS wave function with non-trivial pairing to accurately model the gapless spectrum and edge states in frustrated antiferromagnetic ladders.

Findings

Evidence of a nearly gapless spectrum in frustrated ladders

Edge states localized at boundaries in the system

A new wave function approach capturing the unconventional spin-liquid phase

Abstract

We show strong numerical evidence in favor of an unexpected virtually gapless spectrum, with edge states localized at the boundaries, in frustrated spin-1/2 antiferromagnetic ladders with an odd number of legs. These features can be accurately reproduced by using a projected BCS wave function with a non-trivial pairing, that mixes even and odd reflection symmetries. This approach gives the correct classification of the excitations and provides a simple and very appealing picture of an unconventional spin-liquid phase stabilized by frustration.