Temperature and magnetic field dependence of the lattice constant in spin-Peierls cuprate CuGeO_3 studied by capacitance dilatometry in fields up to 16 Tesla

TL;DR

This study investigates how the lattice constant of CuGeO_3 varies with temperature and magnetic field up to 16 Tesla, revealing structural differences across phases and comparing experimental results with theoretical models.

Contribution

High-resolution measurements of lattice constant changes in CuGeO_3 under magnetic fields, providing detailed phase diagrams and insights into the spin-Peierls transition behavior.

Findings

Structural differences between phases are established.

The phase diagram aligns with Cross Fisher theory but shows deviations.

Spontaneous strain behavior varies with field and phase.

Abstract

We present high resolution measurements of the thermal expansion coefficient and the magnetostriction along the a-axis of CuGeO_3 in magnetic fields up to 16 Tesla. From the pronounced anomalies of the lattice constant a occurring for both temperature and field induced phase transitions clear structural differences between the uniform, dimerized, and incommensurate phases are established. A precise field temperature phase diagram is derived and compared in detail with existing theories. Although there is a fair agreement with the calculations within the Cross Fisher theory, some significant and systematic deviations are present. In addition, our data yield a high resolution measurement of the field and temperature dependence of the spontaneous strain scaling with the spin-Peierls order parameter. Both the zero temperature values as well as the critical behavior of the order parameter are nearly field independent in the dimerized phase. A spontaneous strain is also found in the incommensurate high field phase, which is significantly smaller and shows a different critical behavior than that in the low field phase. The analysis of the temperature dependence of the spontaneous strain yields a pronounced field dependence within the dimerized phase, whereas the temperature dependence of the incommensurate lattice modulation compares well with that of the dimerization in zero magnetic field.