Diverging thermal expansion of the spin-ladder system (C$_5$H$_{12}$N)$_2$CuBr$_4$

TL;DR

This study investigates the thermal expansion and magnetostriction of a spin-ladder compound, revealing complex temperature-dependent behavior and critical phenomena explained by free fermion models and Quantum Monte Carlo simulations.

Contribution

It provides detailed experimental data and theoretical analysis of thermal expansion in a spin-ladder system, achieving quantitative agreement with advanced simulations.

Findings

Thermal expansion exhibits sign changes and a 1/√T divergence at critical fields.

Experimental data aligns semi-quantitatively with free fermion models.

Quantum Monte Carlo simulations match the experimental results quantitatively.

Abstract

We present high-resolution measurements of the $c^\star$-axis thermal expansion and magnetostriction of piperidinium copper bromide \hp. The experimental data at low temperatures is well accounted for by a two-leg spin-ladder Hamiltonian. The thermal expansion shows a complex behaviour with various sign changes and approaches a $1/\sqrt{T}$ divergence at the critical fields. All low-temperature features are semi-quantitatively explained within a free fermion model; full quantitative agreement is obtained with Quantum Monte Carlo simulations.