Thermodynamic Properties and Pressure Effect on the Superconductivity in CaAlSi and SrAlSi

TL;DR

This study investigates the superconducting properties of CaAlSi and SrAlSi under pressure, revealing differences in their electronic structures and how pressure influences their transition temperatures, supported by heat capacity and susceptibility measurements.

Contribution

It provides new insights into the pressure dependence of superconductivity in CaAlSi and SrAlSi, linking experimental results with band structure calculations.

Findings

Heat capacity data aligns with BCS weak-coupling theory.

Superconducting gaps are estimated at 2.7 meV for CaAlSi and 1.4 meV for SrAlSi.

Pressure increases Tc in CaAlSi but decreases it in SrAlSi.

Abstract

Superconductivity in the C32 compounds CaAlSi and SrAlSi is investigated by heat capacity (Cp) measurements as well as high-pressure ac-susceptibility experiments. The heat capacity in the superconducting state is well explained by the BCS theory in the weak-coupling limit. The jump of Cp at the superconducting transition (compared to the normal state electronic heat capacity) is 1.62 and 1.21 for CaAlSi and SrAlSi, respectively, and agrees well with the BCS value of 1.43. The magnitudes of the superconducting gaps are estimated as 2.7 meV (CaAlSi) and 1.4 meV (SrAlSi). The pressure effect on the superconducting transition temperature, dlnTc/dp, is positive in CaAlSi (+0.026 GPa-1) but negative in SrAlSi (-0.024 GPa-1). The opposite sign of the pressure coefficients of Tc indicates distinct differences in the electronic structure and the density of states at the Fermi energy of the two compounds in agreement with recent band structure calculations.