Structural and Magnetic Phase Diagram of CrAs and its Relationship with Pressure-induced Superconductivity

TL;DR

This study maps the magnetic and structural phase diagram of CrAs under pressure, revealing a magnetic transition that coincides with the emergence of superconductivity, highlighting the interplay between magnetism and superconductivity.

Contribution

It provides detailed insights into the pressure-induced magnetic phase transitions in CrAs and their direct link to the onset of superconductivity, a novel understanding for non-collinear helimagnetic superconductors.

Findings

Magnetic reorientation from ab to ac plane at critical pressure

Magnetic order disappears near optimal superconductivity pressure

Antiferromagnetic correlations are crucial for superconductivity

Abstract

Most unconventional superconductors, including cuprates and iron-based superconductors, are derived from chemical doping or application of pressure on their collinearly magnetic-ordered parent compounds[1-5]. The recently discovered pressure-induced superconductor CrAs, as a rare example of a non-collinear helimagnetic superconductor, has therefore generated great interest in understanding microscopic magnetic properties and their interplay with superconductivity [6-8]. Unlike cuprates and iron based superconductors where the magnetic moment direction barely changes upon doping, here we show that CrAs exhibits a spin reorientation from the ab plane to the ac plane, along with an abrupt drop of the magnetic propagation vector at a critical pressure (Pc~0.6 GPa). This magnetic phase transition coincides with the emergence of bulk superconductivity, indicating a direct connection between magnetism and superconductivity. With further increasing pressure, the magnetic order completely disappears near the optimal Tc regime (P~0.94 GPa). Moreover, the Cr magnetic moments between nearest neighbors tend to be aligned antiparallel with increasing pressure toward the optimal superconductivity regime. Our findings suggest that the non-collinear helimagnetic order is strongly coupled to structural and electronic degrees of freedom, and that antiferromagnetic correlations associated with the low magnetic vector phase are crucial for superconductivity.