Resistivity and magnetoresistance of FeSe single crystals under Helium-gas pressure

TL;DR

This study investigates how helium-gas pressure affects the resistivity, phase transition, and magnetoresistance of FeSe single crystals, revealing pressure-dependent shifts in structural and superconducting transition temperatures and Fermi surface reconstruction.

Contribution

It provides detailed measurements of resistivity and magnetoresistance under helium-gas pressure, highlighting the pressure-induced changes in structural and superconducting properties of FeSe.

Findings

The tetragonal-to-orthorhombic transition temperature decreases linearly with pressure.

Superconducting transition temperature increases linearly with pressure.

Resistivity shows different pressure dependencies above and below the structural transition.

Abstract

We present temperature-dependent in-plane resistivity measurements on FeSe single crystals under He-gas pressure up to 800 MPa and magnetic fields $B \leq$ 10 T. A sharp phase transition anomaly is revealed at the tetragonal-to-orthorhombic transition at $T_s$ slightly below 90 K. $T_s$ becomes reduced with increasing pressure in a linear fashion at a rate d$T_{s}$/d$P$ $\simeq$ -31 K/GPa. This is accompanied by a $P$-linear increase of the superconducting transition temperature at $T_c \sim$ 8.6 K with d$T_{c}$/d$P$ $\simeq$ +5.8 K/GPa. Pressure studies of the normal-state resistivity highlight two distinctly different regimes: for $T > T_s$, i.e., in the tetragonal phase, the in-plane resistivity changes strongly with pressure. This contrasts with the state deep in the orthorhombic phase at $T \ll T_s$, preceding the superconducting transition. Here a $T$-linear resistivity is observed the slope of which does not change with pressure. Resistivity studies in varying magnetic fields both at ambient and finite pressure reveal clear changes of the magnetoresistance, $\Delta \rho \propto B^{2}$, upon cooling through $T_s$. Our data are consistent with a reconstruction of the Fermi surface accompanying the structural transition.