Upper critical field and quantum oscillations in tetragonal superconducting FeS

TL;DR

This study investigates the superconducting properties, upper critical field anisotropy, and quantum oscillations in FeS, revealing a quasi-two-dimensional Fermi surface and providing insights into its electronic structure.

Contribution

It presents the first detailed measurements of upper critical fields and quantum oscillations in FeS, combining experimental data with band-structure calculations.

Findings

Superconducting transition temperature T_c = 4.1 K.

Anisotropy ratio of upper critical field Γ(T_c) = 6.9.

Observation of quantum oscillations indicating a quasi-two-dimensional Fermi surface.

Abstract

The magnetoresistance and magnetic torque of FeS are measured in magnetic fields $B$ of up to 18 T down to a temperature of 0.03 K. The superconducting transition temperature is found to be $T_c$ = 4.1 K, and the anisotropy ratio of the upper critical field $B_{c2}$ at $T_c$ is estimated from the initial slopes to be $\Gamma(T_c)$ = 6.9. $B_{c2}(0)$ is estimated to be 2.2 and 0.36 T for $B \parallel ab$ and $c$, respectively. Quantum oscillations are observed in both the resistance and torque. Two frequencies $F$ = 0.15 and 0.20 kT are resolved and assigned to a quasi-two-dimensional Fermi surface cylinder. The carrier density and Sommerfeld coefficient associated with this cylinder are estimated to be 5.8 $\times$ 10$^{-3}$ carriers/Fe and 0.48 mJ/(K$^2$mol), respectively. Other Fermi surface pockets still remain to be found. Band-structure calculations are performed and compared to the experimental results.