New observations concerning the low-temperature properties of the carrier-poor heavy-fermion system Yb4As3

We report low-temperature specific-heat and thermal-expansion results on the carrier-poor system Yb4As3 as well as Yb-4(As1-yXy)(3), X: P, Sb. We infer that Yb4As3 behaves as a two-fluid system with almost decoupled spin and charge excitations. Quasi-one-dimensional spin excitations within S = 1/2 Heisenberg chains of Yb3+ ions formed in the charge-ordered state dominate the low-temperature thermodynamic properties. The effect of a magnetic field is to open a (pseudo-)gap in the low-energy spin-excitation spectrum. The Gruneisen parameter shows rather anomalous temperature and field dependences. (C) 1998 Elsevier Science B.V. All rights reserved.