Two-gap to Single-gap Superconducting Transition on a Honeycomb Lattice in Ca$_{1-x}$Sr$_{x}$AlSi

TL;DR

This study investigates Ca$_{1-x}$Sr$_{x}$AlSi, revealing a tunable transition from two-gap to single-gap superconductivity on a honeycomb lattice influenced by structural buckling.

Contribution

It introduces Ca$_{1-x}$Sr$_{x}$AlSi as a model system for studying tunable superconducting gap structures on honeycomb lattices.

Findings

Demonstrates a two-gap to single-gap transition in superconductivity.

Shows superconductivity is enhanced by structural buckling.

Provides insights into the relationship between lattice structure and superconducting properties.

Abstract

It is a well-established fact that the physical properties of compounds follow their crystal symmetries. This has especially pronounced implications on emergent collective quantum states in materials. Specifically, the effect of crystal symmetries on the properties of superconductors is widely appreciated, although the clarification of this relationship is a core effort of on-going research. Emergent phenomena on honeycomb lattices are of special interest, as they can give rise to spectacular phenomenology, as manifested by the recent discovery of correlated states in magic-angle graphene, or by the high-temperature superconductivity in MgB$_2$. Here, we report on the structural and microscopic superconducting properties of a class of ternary superconductors with Al/Si honeycomb layers, i.e. Ca$_{1-x}$Sr$_{x}$AlSi. We show that this solid solution is a remarkable model system with a highly tunable two-gap to single-gap superconducting system on a honeycomb lattice, where the superconductivity is enhanced by a subtle structural instability, i.e. the buckling of the Al/Si layers.