Multiband character of $\beta$-FeSe: Angular dependence of the magnetoresistance and upper critical field

TL;DR

This study investigates the anisotropic transport properties of $eta$-FeSe single crystals, revealing multiband effects in magnetoresistance and upper critical field behavior through experimental measurements and a two-band model.

Contribution

It provides the first detailed analysis of the angular dependence of magnetoresistance and upper critical field in $eta$-FeSe, demonstrating the importance of multiband effects.

Findings

Strong anisotropic positive magnetoresistance below 90 K

Temperature-dependent anisotropy of the upper critical field

Two-band model successfully describes transport properties

Abstract

We studied $ab$-plane transport properties in single crystals of the superconductor $\beta$-FeSe up to 16 T. In the normal state, below 90 K, the crystals present a strongly anisotropic positive magnetoresistance that becomes negligible above that temperature. In the superconducting state (T$_c$=8.87(5) K) the upper critical field anisotropy $H$$_{c2}$$\parallel$$ab$ / $H$$_{c2}$$\parallel$$c$ changes with temperature and the angular dependence of the dissipation for fixed temperatures and fields reflects a strongly anisotropic behavior. Our results make evident that multiband effects are needed to describe the measured transport properties. We model the magnetoresistance and upper critical field behavior with a two-band model showing that the diffusivities ratio parameter remains unchanged going from the normal to the superconducting state.