Reentrant orbital effect against superconductivity in the quasi-two-dimensional superconductor NbS$_2$

TL;DR

This paper develops a theoretical model for the orbital effects on superconductivity in NbS$_2$, showing how quantum electron motion influences the suppression and potential enhancement of superconductivity under high magnetic fields.

Contribution

The authors derive an integral equation for the superconducting gap considering quantum electron motion in a Q2D superconductor with a tilted magnetic field, and compare it with experimental data.

Findings

Orbital effects partially suppress superconductivity in the Ginzburg-Landau region.

At high magnetic fields (~15 T), orbital effects can enhance the FFLO phase.

Reversible nature of orbital effects against superconductivity in parallel magnetic fields.

Abstract

We derive integral equation for superconducting gap, which takes into account the quantum nature of electron motion in a parallel magnetic field in a quasi-two-dimensional (Q2D) superconductor in the presence of a non-zero perpendicular field component. By comparison of our theoretical results with the recent experimental data obtained on the NbS$_2$, we show that the orbital effect against superconductivity partially destroys superconductivity in the so-called Ginzburg-Landau area of this Q2D conductor, as expected. Nevertheless, at relatively high magnetic fields, $H \simeq 15 \ T$, the orbital effect starts to improve the Fulde-Ferrell-Larkin-Ovchinnikov phase in the NbS$_2$, due to the quantum nature of electron motion in a parallel magnetic field. In our opinion, this is the most clear demonstration that the orbital effect against superconductivity in a parallel magnetic field has a reversible nature.