Heavy-fermion hybridization gap with topological surface states
SmB₆ is a heavy-fermion compound where Sm 4f electrons hybridize with 5d conduction electrons, opening a Kondo hybridization gap V² at the Fermi level. Due to band inversion from spin-orbit coupling, topological surface states appear inside the bulk gap, giving a residual conductance plateau at low temperature. The resistance saturates below ~4 K — a hallmark of the topological surface channel.