Superconductivity enhanced by $d$-band filling in La$T{r}_2$Al${}_{20}$ with $Tr$ = Mo and W

Abstract

Electrical resistivity, magnetic susceptibility, and specific heat measurements on single crystals of La$T{r}_2$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$T{r}_2$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 $RT{r}_2$Al${}_{20}$ are discussed.

15 pages, 8 figures. arXiv admin note: substantial text overlap with arXiv:1802.06119