We have measured the elastic constant (C11-C12)/2 in URu2Si2 by means of high-frequency ultrasonic measurements in pulsed magnetic fields H || [001] up to 61.8 T in a wide temperature range from 1.5 to 116 K. We found a reduction of (C11-C12)/2 that appears only in the temperature and magnetic field region in which URu2Si2 exhibits a heavy-electron state and hidden-order. This change in (C11-C12)/2 appears to be a response of the 5f-electrons to an orthorhombic and volume conservative strain field \epsilon_xx-\epsilon_yy with {\Gamma}3-symmetry. This lattice instability is likely related to a symmetry-breaking band instability that arises due to the hybridization of the localized f electrons with the conduction electrons, and is probably linked to the hidden-order parameter of this compound.
@article{arxiv.1311.3748,
title = {Hybridization-Driven Orthorhombic Lattice Instability in URu2Si2},
author = {T. Yanagisawa and S. Mombetsu and H. Hidaka and H. Amitsuka and M. Akatsu and S. Yasin and S. Zherlitsyn and J. Wosnitza and K. Huang and M. Janoschek and M. B. Maple},
journal= {arXiv preprint arXiv:1311.3748},
year = {2013}
}