{\Gamma}3-type Lattice Instability and the Hidden Order of URu2Si2

TL;DR

This study investigates lattice instabilities in URu2Si2 using ultrasonic measurements under high magnetic fields, revealing a connection between lattice behavior, hybridized electronic states, and the hidden order phase.

Contribution

It provides new experimental evidence linking {b3}3-type lattice instability to both the hybridized electronic state and hidden order in URu2Si2, and discusses limitations of localized-electron models.

Findings

{b3}3-type lattice instability is related to hidden order and hybridized electronic state.

Magnetic field suppresses lattice softening associated with hidden order.

No step-like anomaly observed up to 68.7 T in certain field directions.

Abstract

We have performed ultrasonic measurements on single-crystalline URu2Si2 with pulsed magnetic fields, in order to check for possible lattice instabilities due to the hybridized state and the hidden-order state of this compound. The elastic constant (C11-C12)/2, which is associated with a response to the {\Gamma}3-type symmetry-breaking (orthorhombic) strain field, shows a three-step increase at H > 35 T for H || c at low temperatures, where successive meta-magnetic transitions are observed in the magnetization. We discovered a new fact that the absolute change of the softening of (C11-C12)/2 in the temperature dependence is quantitatively recovered at the suppression of hybridized-electronic state and the hidden order in high-magnetic field for H \perp c associated with the successive transitions. The present results suggest that the {\Gamma}3-type lattice instability, is related to both the emergence of the hybridized electronic state and the hidden-order parameter of URu2Si2. On the other hand, magnetic fields H || [100] and [110] enhance the softening of (C11-C12)/2 in the hidden order phase, while no step-like anomaly is observed up to 68.7 T. We discuss the limitation of the localized-electron picture for describing these features of URu2Si2 by examination of a crystalline electric field model in terms of mean-field theory.