Magnetic excitations and phonon anomalies in URu2Si2

Abstract

The results of a polarized light scattering study of U${\mathrm{Ru}}_2$ ${\mathrm{Si}}_2$ are presented and discussed for the temperature range $5\le T\le 350$ K. Two of the Raman-active phonons allowed by the space- and site-group symmetries of U${\mathrm{Ru}}_2$ ${\mathrm{Si}}_2$ ($D_{4h}^{17}-\frac{14}{\mathrm{mmm}}$) are observed, displaying symmetries $A_{1g}$ and $B_{1g}$. The $A_{1g}$ phonon demonstrates a large integrated intensity increase with decreasing temperature, suggesting a low-temperature increase in the strong electron-phonon coupling. Additionally, quasielastic scattering from spin fluctuations is noted, displaying the symmetry of the antisymmetric representation $A_{2g}$. The spin-fluctuation linewidth is seen to decrease rapidly near $T_N$, alluding to the formation of a gap over much of the Fermi surface.