Electronic structure of low carrier ytterbium pnictides

The charge carriers of Yb4X3, X = P, As, Sb, Bi, are Yb-4f electrons and X- p holes. A very low X-p density of states towards the band maximum in conne ction with a strong Yb-4f onsite Coulomb correlation results in the extreme ly low carrier concentration found in these compounds. Charge ordering amon g the Yb2+ and Yb3+ ions is essential in this respect. Electronic structure calculations are reported which reveal this picture, and which suggest tha t a large part of the strongly enhanced Sommerfeld constant is due to spin excitations in charge ordered chains. (C) 1999 Elsevier Science B.V. All ri ghts reserved.