Anisotropic Kondo pseudo-gap in URu2Si2

Abstract

A polarized electronic Raman scattering study reveals the emergence of symmetry dependence in the electronic Raman response of single crystalline URu${}_2$Si${}_2$ below the Kondo crossover scale $T_K\sim 100K$. In particular, the development of a coherent Kondo pseudo-gap predominantly in the E${}_g$ channel highlights strong anisotropy in the Kondo physics in URu${}_2$Si${}_2$ that has previously been neglected in theoretical models of this system. A calculation of the Raman vertices demonstrates that the strongest Raman vertex does indeed develop within the E${}_g$ channel for interband transitions and reaches a maximum along the diagonals of the Brillouin zone, implying a d-wave-like geometry for the Kondo pseudo-gap. Below the hidden order phase transition at $T_{HO}=17.5K$, the magnitude of the pseudo-gap is found to be enhanced. Moreover, the anisotropy of the pseudo-gap is similar in form to that proposed for the chiral d-wave (E${}_g$) superconducting state that appears below $T_c=1.5K$.