Unconventional superconductivity in the layered iron germanide YFe$_2$Ge$_2$

TL;DR

This paper reports the discovery of intrinsic unconventional superconductivity below 1.8 K in the layered iron germanide YFe₂Ge₂, which has a 3D Fermi surface and strong electronic correlations, expanding the known family of iron-based superconductors.

Contribution

It demonstrates that YFe₂Ge₂ exhibits intrinsic superconductivity outside the known iron pnictide or chalcogenide families, with a 3D Fermi surface unlike typical layered iron superconductors.

Findings

Superconductivity observed below 1.8 K in high-quality YFe₂Ge₂ samples.

YFe₂Ge₂ shows a 3D Fermi surface and strong electronic correlations.

Superconductivity is intrinsic and not due to impurities.

Abstract

Since the discovery of superconductivity in LaFePO in 2006, numerous iron-based superconductors have been identified within diverse structure families, all of which combine iron with a group-V (pnictogen) or group-VI (chalco- gen) element. Unconventional superconductivity is extremely rare among transition metal compounds outside these layered iron systems and the cuprates, and it is almost universally associated with highly anisotropic electronic properties and nearly 2D Fermi surface geometries. The iron-based intermetallic YFe$_2$Ge$_2$ features a 3D Fermi surface and a strongly enhanced low temperature heat capacity, which signals strong electronic correlations. We present data from a new generation of high quality samples of YFe$_2$Ge$_2$, which show superconducting transition anomalies below 1.8 K in thermodynamic as well as transport measurements, establishing that superconductivity is intrinsic in this layered iron compound outside the known superconducting iron pnictide or chalcogenide families. The Fermi surface geometry of YFe$_2$Ge$_2$ resembles that of KFe$_2$As$_2$ in the high pressure collapsed tetragonal phase, in which superconductivity at temperatures as high as 10 K has recently been reported, suggesting an underlying connection between the two systems.