Rattling enhanced superconductivity in MV$_2$Al$_{20}$ (M = Sc, Lu, Y) intermetallic cage compounds

TL;DR

This study investigates superconductivity in MV$_2$Al$_{20}$ compounds, revealing that anharmonic 'rattling' modes of M atoms enhance T$_c$, with the first report of superconductivity in LuV$_2$Al$_{20}$.

Contribution

It provides experimental and theoretical evidence that M-atom rattling modes boost superconductivity in MV$_2$Al$_{20}$ compounds, including the first observation in LuV$_2$Al$_{20}$.

Findings

Superconductivity observed in ScV$_2$Al$_{20}$, LuV$_2$Al$_{20}$, and YV$_2$Al$_{20}$.

LuV$_2$Al$_{20}$ superconductivity reported for the first time.

Rattling modes of M atoms are crucial for enhancing T$_c$.

Abstract

Polycrystalline samples of four intermetallic compounds: MV$_2$Al$_{20}$ (M = Sc, Y, La, and Lu) were synthesized using an arc-melting technique. The crystal structures were analyzed by means of powder x-ray diffraction and Rietveld analysis, and the physical properties were studied by means of heat capacity, electrical resistivity and magnetic susceptibility measurements down to 0.4 K. For ScV$_2$Al$_{20}$, LuV$_2$Al$_{20}$, and YV$_2$Al$_{20}$, superconductivity was observed with critical temperatures T$_c$ = 1.00 K, 0.57 K, and 0.60 K, respectively. Superconductivity for the Lu compound is reported for the first time. Theoretical calculations of the electronic and phonon structures were conducted in order to analyze the superconductivity and dynamics in ScV$_2$Al$_{20}$, YV$_2$Al$_{20}$, and LuV$_2$Al$_{20}$ and to explain the lack of a superconducting transition in LaV$_2$Al$_{20}$ down to 0.4 K. The results of the experimental and theoretical studies show that all the compounds are weakly-coupled type II BCS superconductors, and reveal the importance of the M-atom anharmonic "rattling" modes for the superconductivity in these materials, which seem to enhance T$_c$, especially for ScV$_2$Al$_{20}$.