Complexity in the hybridization physics revealed by depth-resolved photoemission spectroscopy of single crystalline novel Kondo lattice systems, CeCuX$_2$ (X = As/Sb)

Abstract

We investigate the electronic structure of a novel Kondo lattice system CeCuX2 (X = As/Sb) employing high resolution depth-resolved photoemission spectroscopy of high quality single crystalline materials. CeCuSb2 and CeCuAs2 represent different regimes of the Doniach phase diagram exhibiting Kondo-like transport properties and CeCuSb2 is antiferromagnetic (TN ~ 6.9 K) while CeCuAs$_2$ does not show long-range magnetic order down to the lowest temperature studied. In this study, samples were cleaved in ultrahigh vacuum before the photoemission measurements and the spectra at different surface sensitivity establish the pnictogen layer having squarenet structure as the terminated surface which is weakly bound to the other layers. Cu 2p and As 2p spectra show spin-orbit split sharp peaks along with features due to plasmon excitations. Ce 3d spectra exhibit multiple features due to the hybridization of the Ce 4f/5d states with the valence states. While overall lineshape of the bulk spectral functions look similar in both the cases, the surface spectra are very different; the surface-bulk difference is significantly weaker in CeCuAs2 compared to that observed in CeCuSb2. A distinct low binding energy peak is observed in the Ce 3d spectra akin to the scenario observed in cuprates and manganites due to the Zhang-Rice singlets and/or high degree of itineracy of the conduction holes. The valence band spectra of CeCuSb$_2$ manifest highly metallic phase. In CeCuAs2, intensity at the Fermi level is significantly small suggesting a pseudogap-type behavior. These results bring out an interesting scenario emphasizing the importance and subtlety of hybridization physics underlying the exoticity of this novel Kondo system