Superconductivity enhanced by $d$-band filling in La$Tr_2$Al$_{20}$ with $Tr$ = Mo and W

TL;DR

This study investigates how $d$-band filling influences superconductivity in La$Tr_2$Al$_{20}$ compounds with $Tr$ = Mo and W, revealing that increased $4d$ and $5d$ electron filling enhances $T_c$ and superconducting properties.

Contribution

It demonstrates a direct correlation between $d$-band filling and superconducting transition temperature, highlighting the role of $e_g$ orbital filling in superconductivity enhancement.

Findings

La$Tr_2$Al$_{20}$ exhibits superconductivity with $T_c$ up to 3.22 K.

Higher $4d$ and $5d$ electron counts correlate with increased $T_c$ and specific heat.

$d$-electron filling influences the superconducting condensation energy.

Abstract

Electrical resistivity, magnetic susceptibility, and specific heat measurements on single crystals of La$Tr_2$Al$_{20}$ with $Tr$ = Mo and W revealed that these compounds exhibit superconductivity with transition temperatures $T_c$ = 3.22 and 1.81 K, respectively, achieving the highest values in the reported La$Tr_2$Al$_{20}$ compounds. There appears a positive correlation between $T_c$ and the electronic specific heat coefficient, which increases with increasing the number of $4d$- and $5d$-electrons. This finding indicates that filling of the upper $e_g$ orbitals in the $4d$ and $5d$ bands plays an essential role for the significant enhancement of the superconducting condensation energy. Possible roles played by the $d$ electrons in the strongly correlated electron phenomena appearing in $RTr_{2}$Al$_{20}$ are discussed.