Evolution of Heterogeneous Antiferromagnetic State in URu2Si2: Study of Hydrostatic-Pressure, Uniaxial-Stress and Rh-Dope Effects

TL;DR

This study investigates how hidden order in URu2Si2 transitions to antiferromagnetic order under pressure, stress, and doping, revealing a phase change linked to lattice strain and quadrupole order.

Contribution

It provides experimental evidence and analysis of the phase transition mechanisms between hidden order and antiferromagnetism in URu2Si2, emphasizing the role of lattice strain and quadrupole moments.

Findings

Hidden order is replaced by AF order under pressure, stress, and Rh doping.

The phase transition correlates with a 0.1% increase in c/a ratio.

Magnetic excitations vanish in the AF phase, supporting quadrupole order hypothesis.

Abstract

We have investigated the nature of the competition between hidden order and antiferromagnetic (AF) order in URu_2Si_2 by performing the neutron scattering experiments under hydrostatic-pressure P, uniaxial-stress sigma, and Rh-substitution conditions. Hidden order observed at ambient pressure in pure URu_2Si_2 is found to be replaced by the AF order by applying P, sigma along the tetragonal basal plane, and by doping Rh. We discuss these experimental results on the basis of the crystalline strain calculations, and suggest that this phase transition is generated by the 0.1% increase of the tetragonal c/a ratio. We have also found that the magnetic excitation observed in the hidden order phase vanishes in the AF phase. We show that this variation can be qualitatively explained by assuming the hidden order parameter to be quadrupole.