Field-induced length changes in the spin-liquid candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$

TL;DR

This study investigates how magnetic fields influence lattice changes in the spin-liquid candidate $ppa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, revealing field-induced anomalies near 8.7 K that suggest complex magnetic-lattice interactions.

Contribution

It provides the first detailed analysis of magnetic field effects on lattice parameters in this spin-liquid material, highlighting a field-dependent anomaly near 8.7 K.

Findings

Anisotropic lattice effects around 6 K linked to spin-liquid instability.

Magnetic fields along the in-plane b-axis induce a jump-like anomaly at 8.7 K.

The anomaly's characteristics suggest a non-hysteretic, possibly phase transition-like behavior.

Abstract

Measurements of the coefficient of thermal expansion on the spin-liquid candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ have revealed distinct and strongly anisotropic lattice effects around 6 K - a possible spin-liquid instability. In order to study the effects of a magnetic field on the low-temperature spin-liquid state, dilatometric measurements have been conducted both as a function of temperature at \emph{B} = const. and as a function of field at \emph{T} = const. While the 6 K anomaly is found to be insensitive to magnetic fields \emph{B} $\leq$ 10 T, the maximum field applied, surprisingly strong \emph{B}-induced effects are observed for magnetic fields applied along the in-plane \emph{b}-axis. Above a threshold field of 0.5 T < \emph{B}$_c$ $\leq$ 1 T, a jump-like anomaly is observed in the \emph{b}-axis lattice parameter. This anomaly, which is located at 8.7 K at \emph{B} = 1 T, grows in size and shifts to lower temperatures with increasing the magnetic field. Although the anomaly bears resemblance to a first-order phase transition, the lack of hysteresis suggests otherwise.