Anisotropic thermal expansion of Fe1.06Te and FeTe0.5Se0.5 single crystals

TL;DR

This study investigates the anisotropic thermal expansion and heat capacity of Fe1.06Te and FeTe0.5Se0.5 single crystals, revealing phase transitions and contrasting effects of uniaxial pressure on superconductivity.

Contribution

It provides detailed measurements of anisotropic thermal expansion and heat capacity, and analyzes the uniaxial pressure effects on superconducting transition temperatures in these materials.

Findings

Thermal expansion is anisotropic in both materials.

Uniaxial pressure derivatives of Tc have opposite signs for in-plane and c-axis pressures in FeTe0.5Se0.5.

Magnetic contributions dominate the Gruneisen parameter at low temperatures in Fe1.06Te.

Abstract

Heat capacity and anisotropic thermal expansion was measured for Fe1.06Te and FeTe0.5Se0.5 single crystals. Previously reported phase transitions are clearly seen in both measurements. In both cases the thermal expansion is anisotropic. The uniaxial pressure derivatives of the superconducting transition temperature in FeTe0.5Se0.5 inferred from the Ehrenfest relation have opposite signs for in-plane and c-axis pressures. Whereas the Gruneisen parameters for both materials are similar and only weakly temperature-dependent above ~ 80 K, at low temperatures (in the magnetically ordered phase) the magnetic contribution to the Gruneisen parameter in Fe1.06Te is significantly larger than electron and phonon contributions combined.