Quantum oscillations and upper critical magnetic field of the iron-based superconductor FeSe

TL;DR

This study investigates quantum oscillations and the upper critical magnetic field of FeSe, revealing Fermi surface reconstruction, multiband effects, and the dominance of a single band in superconductivity under magnetic fields.

Contribution

It provides detailed measurements of quantum oscillations and $H_{c2}$ in FeSe, demonstrating Fermi surface changes and the role of a primary band in superconductivity, with implications for understanding iron-based superconductors.

Findings

Fermi surface reconstruction at low temperature

Single band mainly controls superconductivity in magnetic fields

Pauli paramagnetic effects significant for in-plane magnetic field

Abstract

Shubnikov-de Haas (SdH) oscillations and upper critical magnetic field ($H\_{c2}$) of the iron-based superconductor FeSe ($T\_c$ = 8.6 K) have been studied by tunnel diode oscillator-based measurements in magnetic fields of up to 55 T and temperatures down to 1.6 K. Several Fourier components enter the SdH oscillations spectrum with frequencies definitely smaller than predicted by band structure calculations indicating band renormalization and reconstruction of the Fermi surface at low temperature, in line with previous ARPES data. The Werthamer-Helfand-Hohenberg model accounts for the temperature dependence of $H\_{c2}$ for magnetic field applied both parallel (\textbf{H} $\|$ $ab$) and perpendicular (\textbf{H} $\|$ $c$) to the iron conducting plane, suggesting that one band mainly controls the superconducting properties in magnetic fields despite the multiband nature of the Fermi surface. Whereas Pauli pair breaking is negligible for \textbf{H} $\|$ $c$, a Pauli paramagnetic contribution is evidenced for \textbf{H} $\|$ $ab$ with Maki parameter $\alpha$ = 2.1, corresponding to Pauli field $H\_{P}$ = 36.5 T