Superconductivity in Ternary Germanite TaAl$_{x}$Ge$_{2-x}$ with a C40 chiral structure

TL;DR

This study discovers a new family of chiral intermetallic superconductors, TaAl$_{x}$Ge$_{2-x}$, with superconductivity emerging at specific Al substitution levels and linked to lattice constant changes.

Contribution

It reports the synthesis and characterization of a novel chiral superconductor family with tunable properties via Al substitution.

Findings

Superconductivity observed at x=0.2 to 0.4 with T_c of 2.0-2.2 K.

Superconductivity suppressed outside the x=0.2 to 0.4 range.

Superconductivity emergence correlates with lattice constant changes.

Abstract

We report a new family of chiral intermetallic superconductors TaAl$_{x}$Ge$_{2-x}$. The mother compound TaGe$_2$ has a C40-type chiral hexagonal crystal structure with a pair of enantiomorphic space groups of $P6{_2}22$ and $P6{_4}22$. By substituting Ge with Al, TaAl$_{x}$Ge$_{2-x}$ polycrystals with the C40 structure were synthesized with Al substitution $x$ from 0 to 0.8. Magnetic susceptibility, magnetization curves and electrical resistivity revealed that TaAl$_{x}$Ge$_{2-x}$ with $x$ of 0.2 to 0.4 was a type-II superconductor with a superconducting transition temperature $T_{\rm c}$ of 2.0 to 2.2 K. The superconductivity disappeared or was largely suppressed at $x$ less than 0.2 and more than 0.4, although all the measurements were performed at temperatures above 1.8 K. An emergence of superconductivity is discussed in terms of the lattice constants changes with the Al substitution.