Photoemission Insight into Heavy-Fermion Behavior in ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$

As shown by angle-resolved photoemission (PE), hybridization of bulk Yb $4f^{2+}$ states with a shallow-lying valence band of the same symmetry leads in ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$ to dispersion of a $4f$ PE signal in the region of the Kondo resonance with a Fermi-energy crossing close to $\overline{\Gamma }$. Additionally, renormalization of the valence state results in the formation of a heavy band that disperses parallel to the $4f$ originating signal. The symmetry and character of the states are probed by circular dichroism and the photon-energy dependence of the PE cross sections.

Figure 1

Experimental geometry.

Figure 2

(a) PE data taken with $h\nu =55\mathrm{eV}$ along $\overline{\Gamma }-\overline{X}(0.78{\AA }^{-1})$. Light areas correspond to high PE intensity. (b) Results of slab calculations (solid lines). Thick stripes are a guide to the eye to emphasize the electronic structure traced in the experiment. Note, rescaling of the ${\mathbf{k}}_{\parallel }$ axis is necessary for quantitative comparison with the experiment that is caused by the neglect of the $4f$ states at $E_F$ in the calculations. Points $\mathbf{A}$ and $\mathbf{B}$ mark electronic states used for the CDAD calculations.

Figure 3

PE plot taken at $h\nu =110\mathrm{eV}$. Inset depicts a top view graph of the same data.

Figure 4

PE data taken with (a) ${\mathrm{I}}_{+}$ and (b) ${\mathrm{I}}_{-}$ light polarization, $h\nu =55\mathrm{eV}$. (c) Intensity difference (${\mathrm{I}}_{+}\mathrm{\text{−}}{\mathrm{I}}_{-}$). Black areas denote regions devoid of dichroism. (d) CDAD calculated for states $\mathbf{A}$ (blue) and $\mathbf{B}$ (red) marked in Fig. 2b, Ref. 17.