Superconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga)

TL;DR

This study revisits the AxV2Al20 cage compound, revealing how low-energy atomic vibrations influence its superconducting properties, with new insights into Einstein-mode vibrations and electron coupling.

Contribution

It demonstrates the relationship between low-energy Einstein-mode vibrations and superconductivity in AxV2Al20, highlighting the role of specific atomic vibrations in electronic behavior.

Findings

Superconductivity observed below 1.66 K for Al and Ga variants.

Low-energy Einstein modes detected at 24 K (Al) and 8 K (Ga).

Enhanced resistivity linked to coupling between vibrations and electrons.

Abstract

A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin and coworkers 40 years ago, is revisited to investigate the low-energy, local vibrations of the A atoms and their influence on the electronic and superconducting properties of the compound. Polycrystalline samples with A = Al, Ga, Y, and La are studied through resistivity and heat capacity measurements. Weak-coupling BCS superconductivity is observed below Tc = 1.49, 1.66, and 0.69 K for Ax = Al0.3, Ga0.2, and Y, respectively, but not above 0.4 K for Ax = La. Low-energy modes are detected only for A = Al and Ga, which are approximately described by the Einstein model with Einstein temperatures of 24 and 8 K, respectively. A weak but significant coupling between the low-energy modes, which are almost identical to those called rattling in recent study, and conduction electrons manifests itself as anomalous enhancement in resistivity at around low temperatures corresponding to the Einstein temperatures.