Pressure effects on the electronic properties of the undoped superconductor ThFeAsN

TL;DR

This study investigates how applying pressure up to 3 GPa affects the electronic and magnetic properties of the undoped ThFeAsN superconductor, revealing a decrease in critical temperature and magnetic transition temperature linked to band structure changes.

Contribution

It provides the first microscopic analysis of pressure effects on ThFeAsN, demonstrating the relationship between pressure, electronic structure, and superconducting properties in this material.

Findings

Pressure reduces Tc and Tm at about -1.1 K/GPa.

Evidence supports a multi-band s±-wave gap symmetry.

Band-structure deformation explains Tc suppression.

Abstract

The recently synthesized ThFeAsN iron-pnictide superconductor exhibits a $T_c$ of 30 K, the highest of the 1111-type series in absence of chemical doping. To understand how pressure affects its electronic properties, we carried out microscopic investigations up to 3 GPa via magnetization, nuclear magnetic resonance, and muon-spin rotation experiments. The temperature dependence of the ${}^{75}$As Knight shift, the spin-lattice relaxation rates, and the magnetic penetration depth suggest a multi-band $s^{\pm}$-wave gap symmetry in the dirty limit, while the gap-to-$T_c$ ratio $\Delta/k_\mathrm{B}T_c$ hints at a strong-coupling scenario. Pressure modulates the geometrical parameters, thus reducing $T_c$, as well as $T_m$, the temperature where magnetic-relaxation rates are maximized, both at the same rate of approximately -1.1 K/GPa. This decrease of $T_c$ with pressure is consistent with band-structure calculations, which relate it to the deformation of the Fe 3$d_{z^2}$ orbitals.