Phonon density of states, anharmonicity, electron-phonon coupling and possible multigap superconductivity in the clathrate superconductors Ba8Si46 and Ba24Si100: Why is Tc different in these two compounds?

TL;DR

This study investigates the phonon properties, electron-phonon interactions, and anharmonic effects in Ba8Si46 and Ba24Si100 to understand why their superconducting transition temperatures differ significantly.

Contribution

It provides a comprehensive analysis of phonon density of states and electron-phonon coupling to explain the Tc variation between the two silicon clathrate superconductors.

Findings

Different phonon spectra influence Tc in the two compounds.

Anharmonicity and electron-phonon coupling are key factors in superconductivity.

Structural differences affect phonon behavior and superconducting properties.

Abstract

We report a detailed study of specific heat, electrical resistivity and thermal expansion in combination with inelastic neutron and inelastic X-ray scattering to investigate the origin of superconductivity in the two silicon clathrate superconductors Ba8Si46 and Ba24Si100. Both compounds have a similar structure based on encaged barium atoms in oversized silicon cages. However, the transition temperatures are rather different: 8 K and 1.5 K respectively. By extracting the superconducting properties, phonon density of states, electron-phonon coupling function and phonon anharmonicity from these measurements we discuss the important factors governing Tc and explain the difference between the two compounds.