Thermodynamic Properties of the Incommensurate Phase of CuGeO_3

TL;DR

This study investigates the thermodynamic behavior of CuGeO_3 in its incommensurate phase under high magnetic fields, revealing anomalies at phase transitions, magnetic excitation effects, and detailed strain and structural distortion data.

Contribution

It provides high-resolution measurements of specific heat and thermal expansion in CuGeO_3 under magnetic fields, elucidating the incommensurate phase's thermodynamic and structural properties.

Findings

Pronounced anomalies at phase transition allow pressure dependency analysis.

Specific heat follows a T^3 law at low temperatures in high magnetic fields.

Spontaneous strains are reduced but similar in anisotropy and temperature dependence to zero field.

Abstract

We present high resolution measurements of the specific heat and the thermal expansion of the inorganic spin--Peierls cuprate CuGeO_3 in a magnetic field of 16 Tesla. At the transition from the incommensurate to the uniform phase both quantities show pronounced anomalies, which allow to derive the uniaxial pressure dependencies of the transition temperature. In high magnetic fields the specific heat is dominated by magnetic excitations and follows a T^3 law at low temperatures. The thermal expansion measurements show the occurrence of spontaneous strains along all three lattice constants and yield high resolution measurements of the temperature dependence of the incommensurate structural distortion. The sizes of the spontaneous strains in the incommensurate phase are significantly reduced, but both their anisotropy as well as their temperature dependencies are very similar to those in zero field.