Low energy excitation spectrum and Cu(2) spin-lattice relaxation from the singlet correlated band in YBa2Cu4O8

Abstract

We report the low energy excitation spectrum and the spin-lattice relaxation for the planar Cu of the high Tc superconductor YBa2Cu4O8. We use a three band Hubbard model. Its singlet band exhibits a well-established saddle point of strong copper character. The susceptibility is governed by a Fermi-liquid like contribution coming from thermally activated copper holes in this saddle point. By comparing our calculated and experimental results, we can conclude that in YBa2Cu4O8 the low energy physics is determined by a high density of charge excitations in the singlet impurity band together with spin excitations in the lower Hubbard band. © 1994.