Anisotropic s-wave superconductivity in single crystals CaAlSi from penetration depth measurements

TL;DR

This study investigates the anisotropic superconducting gap in CaAlSi single crystals through penetration depth measurements, revealing a prolate spheroidal gap with varying anisotropy depending on the critical temperature.

Contribution

It provides the first detailed analysis of the anisotropic superconducting gap structure in CaAlSi using penetration depth data and BCS modeling.

Findings

Prolate spheroidal gap structure consistent with BCS theory.

Gap anisotropy decreases with increasing T_c.

Weak coupling in the ab-plane and stronger coupling along the c-axis.

Abstract

In- and out-of-plane London penetration depths were measured in single crystals CaAlSi (T_{c}=6.2 K and 7.3 K) using a tunnel-diode resonator. A full 3D BCS analysis of the superfluid density is consistent with a prolate spheroidal gap, with a weak-coupling BCS value in the ab-plane and stronger coupling along the c-axis. The gap anisotropy was found to significantly decrease for higher T_{c} samples.