Pressure-temperature phase diagram of the heavy-electron superconductor URu2Si2

TL;DR

This study maps the pressure-temperature phase diagram of URu2Si2, revealing how antiferromagnetic and superconducting phases evolve under pressure, and clarifies their coexistence and relationship with hidden order phases.

Contribution

It provides detailed experimental data on the pressure-induced magnetic phases and their impact on superconductivity in URu2Si2, advancing understanding of its complex phase diagram.

Findings

Antiferromagnetic order sharply increases above 0.7 GPa.

Superconductivity is suppressed as antiferromagnetic order develops.

Multiple parasitic magnetic phases are identified and characterized.

Abstract

The pressure-temperature phase diagram of the heavy-electron superconductor URu2Si2 has been reinvestigated by ac-susceptibility and elastic neutron-scattering (NS) measurements performed on a small single-crystalline rod (2 mm in diameter, 6 mm in length) in a Cu-Be clamp-type high-pressure cell (P < 1.1 GPa). At ambient pressure, this sample shows the weakest antiferromagnetic (AF) Bragg reflections reported so far, corresponding to the volume-averaged staggered moment of mord ~ 0.011 mB/U. Under applied pressure, the AF scattering intensity exhibits a sharp increase at P ~ 0.7 GPa at low temperatures. The saturation value of the AF scattering intensity above 0.7 GPa corresponds to mord ~ 0.41 mB/U, which is in good agreement with that (~ 0.39 mB/U) observed above 1.5 GPa in our previous NS measurements. The superconductivity is dramatically suppressed by the evolution of AF phase, indicating that the superconducting state coexists only with the hidden order phase. The presence of parasitic ferro- and/or antiferromagnetic phases with transition temperatures T1star =120(5) K, T2star = 36(3) K and T3star = 16.5(5) K and their relationship to the low-T ordered phases are also discussed.