Surface density of states of layered $f$-electron materials

We theoretically analyze the surface density of states of heavy fermion materials such as CeCoIn${}_5$. Recent experimental progress has made it possible to locally probe the formation of heavy quasiparticles in these systems via scanning tunneling microscopy, in which strongly temperature-dependent resonances at the Fermi energy have been observed. The shape of these resonances varies depending on the surface layer, i.e., if cerium or cobalt terminates the sample. We clarify the microscopic origin of this difference by taking into account the layered structure of the material. Our simple model explains all the characteristic properties observed experimentally, such as a layer-dependent shape of the resonance at the Fermi energy, displaying a hybridization gap for the cerium layer and a peak or dip structure for the other layers. Our proposal resolves the seemingly unphysical assumptions in the preceding analysis based on the two-channel cotunneling model.

Figure 1

Crystal structure of CeCoIn${}_5$.

Figure 2

Temperature-dependent LDOS close to the Fermi energy, $\omega =0$, for a system with a Ce surface layer. The temperatures are scaled so that the Kondo temperature of the simulated system is 50 K, corresponding to CeCoIn${}_5$. The right inset shows the shape of the whole simulated band. The left inset shows the simplified lattice we have used to simulate the spectra.

Figure 3

Same as Fig. 2, but for a lattice corresponding to the Co layer in CeCoIn${}_5$.