Disorder instability of the magnon condensate in a frustrated spin ladder

TL;DR

This study investigates how even minimal disorder disrupts the magnon condensate in a frustrated spin ladder, revealing its extreme fragility due to random frustration effects.

Contribution

It demonstrates that small chemical substitutions can destroy the magnon condensate phase transition, highlighting the sensitivity of quantum magnetic states to disorder.

Findings

Bond randomness destroys the magnon condensate at x=0.01

The magnon condensate is highly fragile to disorder

Disorder induces random frustration in the incommensurate state

Abstract

The effect of disorder is studied on the field-induced quantum phase transition in the frustrated spin-ladder compound H8C4SO2Cu2(Cl[1-x]Brx)4 using bulk magnetic and thermodynamic measurements. The parent material (x=0) is a quantum spin liquid, which in applied fields is known to form a magnon condensate with long-range helimagnetic order. We show that bond randomness introduced by a chemical substitution on the non-magnetic halogene site destroys this phase transition at very low concentrations, already for x=0.01. The extreme fragility of the magnon condensate is attributed to random frustration in the incommensurate state.