Temperature-dependent high-resolution photoemission study of the Kondo insulator YbB12

We have performed a detailed temperature-dependent photoemission study of the conduction-band states in the Kondo insulator YbB12 using single crystalline samples. Measurements with improved energy resolution have revealed (pseudo)gaps of two energy scales. The size of the narrower gap similar to 10 meV and its disappearance at high temperatures are consistent with the temperature dependence of the electrical resistivity and the magnetic susceptibility. The larger pseudogap of similar to 100 meV depends on temperature even at room temperature. We discuss how the characteristics of the Kondo insulator are reflected in the conduction-band photoemission spectra.