Pressure Induced Stripe-order Antiferromagnetism and First-order Phase Transition in FeSe

TL;DR

This study reveals that applying pressure to FeSe induces stripe-order antiferromagnetism and a first-order phase transition, highlighting a strong coupling between nematicity and magnetism in this iron-based superconductor.

Contribution

It provides direct experimental evidence of pressure-induced stripe-order antiferromagnetism and a first-order transition in FeSe, supporting magnetic-driven nematicity.

Findings

Suppression of structural transition temperature with pressure.

Emergence of stripe-order antiferromagnetism above 2 GPa.

Magnetic phase transition is first-order.

Abstract

To elucidate the magnetic structure and the origin of the nematicity in FeSe, we perform a high-pressure $^{77}$Se NMR study on FeSe single crystals. We find a suppression of the structural transition temperature with pressure up to about 2 GPa from the anisotropy of the Knight shift. Above 2 GPa, a stripe-order antiferromagnetism that breaks the spatial four-fold rotational symmetry is determined by the NMR spectra under different field orientations and with temperatures down to 50 mK. The magnetic phase transition is revealed to be first-order type, implying the existence of a concomitant structural transition via a spin-lattice coupling. Stripe-type spin fluctuations are observed at high temperatures, and remain strong with pressure. These results provide clear evidences for strong coupling between nematicity and magnetism in FeSe, and therefore support a universal scenario of magnetic driven nematicity in iron-based superconductors.