Ultrahigh-resolution and angle-resolved photoemission study of SmB6

The photoemission spectra with the ultrahigh-energy resolution reveal the small gap formation at lower temperatures than the characteristic coherent temperature T coh . In addition, the temperature dependence of the density of states at Fermi level clearly shows a simple scaling relationship with T coh . The narrow 4f-band with a very small dispersion just below E F are observed by angle-resolved spectra at the first time.