Elastic constants of URu2Si2 in magnetic fields

In previous ultrasonic measurements on the tetragonal compound URu2Si2 in z ero magnetic field, we found a tendency of the softening below similar to 7 0 K in the transverse 1/2(c(11) - c(12)) mode. The results strongly suggest the presence of the lattice instability in this system. We here present th e experimental results of the temperature dependence of elastic constants, c(11-) 1/2(c(11) - c(12)) and c(66) in magnetic fields along the tetragonal c-axis up to 12 T. The 1/2(c(11) - c(12)) mode increases as the magnetic f ield is increased, while the c(11) and c(66) modes decrease. The small but distinct held effects imply that the elastic anomaly in the transverse mode is caused by electrons. (C) 2000 Published by Elsevier Science B.V. All ri ghts reserved.