Anomalous features in the photo-emission spectrum of heavy-fermion semiconductors

The heavy-fermion semiconductors have a low-temperature insulating state th at is characterized by an anomalously small energy gap, varying between 10 and 100 K. The small gap is a many-body renormalized hybridization gap. The dispersion and temperature dependence of the electronic spectral density o f states is calculated, using the large U-ff limit of the N-fold degenerate Anderson lattice model at half-filling, together with a slave boson 1/N ex pansion. The effect of emission and absorption of the slave boson fluctuati ons is to produce a dispersive asymmetric f(0) peak, and a thermally activa ted broadening of the f quasi-particle peak in A(k,omega). As the temperatu re is reduced the structure in the vicinity of the Fermi-energy sharpens up . The theory is compared to experiments on the materials FeSi and Ce3Bi4Pt3 . (C) 1999 Elsevier Science B.V. All rights reserved.