Thermodynamics of the coupled spin-dimer system TlCuCl3 close to a quantum phase transition

TL;DR

This study investigates the thermodynamic properties of TlCuCl3 near its quantum phase transition, revealing large pressure effects and divergence of the Grueneisen parameter, with some discrepancies from theoretical predictions.

Contribution

It provides detailed experimental measurements of thermal expansion, magnetostriction, and specific heat near the quantum critical point, highlighting pressure dependencies and deviations from theory.

Findings

Huge pressure dependencies of the spin gap.

Diverging Grueneisen parameter near critical field.

Discrepancies between experimental data and theoretical predictions.

Abstract

We present thermal expansion alpha, magnetostriction and specific heat C measurements of \tal, which shows a quantum phase transition from a spin-gap phase to a Neel-ordered ground state as a function of magnetic field around H_{C0}->4.8T. Using Ehrenfest's relation, we find huge pressure dependencies of the spin gap for uniaxial as well as for hydrostatic pressure. For T->0 and H->H_{C0} we observe a diverging Grueneisen parameter Gamma(T)=alpha/C, in qualitative agreement with theoretical predictions. However, the predicted individual temperature dependencies alpha(T) and C(T) are not reproduced by our experimental data.