Field-concentration phase diagram of a quantum spin liquid with bond defects

TL;DR

This study maps the phase diagram of a quantum spin liquid with bond defects, revealing how chemical disorder influences magnetic properties and phase transitions under high magnetic fields.

Contribution

It provides a systematic analysis of the field-temperature and field-concentration phase diagrams for a disordered quantum spin liquid, highlighting differences from previous studies and the effects of chemical substitution.

Findings

Disorder affects the magnetic phase diagram significantly.

Chemical substitution modifies magnetic excitation spectra.

Results challenge previous findings on the parent compound.

Abstract

The magnetic susceptibility of the gapped quantum spin liquid compound (C$_4$H$_{12}$N$_2$)Cu$_2$Cl$_6$ and its chemically disordered derivatives (C$_4$H$_{12}$N$_2$)Cu$_2$(Cl$_{1-x}$Br$_{x}$)$_6$ are systematically studied in magnetic fields of up to 45 T, as a function of Br concentration. The corresponding field-temperature and field-concentration phase diagrams are determined. Measurements on the disorder-free parent compound are not fully consistent with previously published results by other authors [PRL{\bf 96}, 257203 (2006)]. The effect of Br/Cl substitution on the magnetic properties is superficially similar to that of finite temperature. However, important differences are identified and discussed with reference to the previously studied magnetic excitation spectra.