The crystalline lattice of URu_2Si_2 under pressure in the paramagnetic, hidden order, and antiferromagnetic states

TL;DR

This study uses X-ray diffraction under pressure to examine how the crystal lattice of URu2Si2 responds to hidden order and antiferromagnetic transitions, revealing subtle lattice coupling and anisotropic compression effects.

Contribution

It provides detailed insights into the pressure-dependent lattice behavior of URu2Si2, confirming the robustness of its structure and revealing subtle coupling with electronic transitions.

Findings

The crystal structure remains stable under pressure.

Lattice parameters show anisotropic compression with decreasing c/a ratio.

The bulk modulus is estimated at approximately 190 GPa.

Abstract

X-ray diffraction experiments under pressure in a diamond anvil cell have been performed to gauge any response of the crystalline lattice of URu2Si2 to the "hidden order" or antiferromagnetic transitions, the latter of which is accessible only with applied pressure. The ambient-pressure crystal structure of URu2Si2 persists to high pressure, and structural characterization reveals a reasonably robust crystal lattice with respect to both of the aforementioned temperature-induced electronic transitions. Coupling between the lattice and the "hidden order" transition is reconfirmed to be subtle, and that subtle sensitivity is extended to the antiferromagnetic transition. The pressure-dependent evolution of the lattice parameters indicates a slightly anisotropic compression of the unit cell, which results in a decrease in the lattice c/a ratio with increasing pressure. From compression data, the bulk modulus is estimated to be B_0~190 GPa. While the unit cell volume undergoes compression, the Ru-Si layers separating the U planes evince an apparent "flattening," resulting in a more 2D-like structure and an increased volume per U ion.