Unconventional bulk superconductivity in YFe$_2$Ge$_2$ single crystals

TL;DR

This study reports the synthesis of high-quality YFe₂Ge₂ single crystals with reduced disorder, revealing unconventional superconductivity characterized by a sign-changing order parameter and in-gap states, enabling detailed investigations of its normal and superconducting states.

Contribution

Developed a new crystal growth method for YFe₂Ge₂, achieving significantly reduced disorder and enabling detailed study of its unconventional superconducting properties.

Findings

High-quality crystals with low residual resistivity and sharp heat capacity anomalies

Evidence of in-gap states consistent with a sign-changing order parameter

Enhanced potential for multi-probe investigations of superconductivity in YFe₂Ge₂

Abstract

Using a new horizontal flux growth technique to produce high quality crystals of the unconventional superconductor YFe$_2$Ge$_2$ has led to a seven-fold reduction in disorder scattering, resulting in mm-sized crystals with residual resistivities $\simeq \SI{0.45}{\micro\ohm\centi\meter}$, resistivity ratios $\simeq 430$ and sharp superconducting heat capacity anomalies. This enables searching multi-probe experiments investigating the normal and superconducting states of YFe$_2$Ge$_2$. Low temperature heat capacity measurements suggest a significant residual Sommerfeld coefficient, consistent with in-gap states induced by residual disorder as predicted for a sign-changing order parameter.