Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

TL;DR

This paper investigates how small changes in growth conditions affect the morphology, transition temperatures, and residual resistivity ratio in vapor-grown FeSe, revealing disorder's key role in its superconducting and structural properties.

Contribution

It demonstrates that disorder, rather than composition, significantly influences the superconducting transition temperature and structural transition in FeSe.

Findings

Tc varies from 8.8 K to 3 K with growth conditions.

Residual resistivity ratio correlates with Tc.

Structural transition temperature Ts is disorder-dependent.

Abstract

The study of the iron-based superconductor FeSe has blossomed with the availability of high quality single crystals, obtained through flux/vapor-transport growth techniques below the structural transformation temperature of its tetragonal phase, T~450 C. Here, we report on the variation of sample morphology and properties due to small modifications in the growth conditions. A considerable variation of the superconducting transition temperature Tc, from 8.8 K to 3 K, which cannot be correlated with the sample composition, is observed. Instead, we point out a clear correlation between Tc and disorder, as measured by the residual resistivity ratio. Notably, the tetragonal-to-orthorhombic structural transition is also found to be quite strongly disorder dependent (Ts =72 - 90 K), and linearly correlated with Tc.