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

Abstract We report low-temperature specific-heat and thermal-expansion results on the carrier-poor system Yb 4 As 3 as well as Yb 4 (As 1− y X y ) 3 , X: P, Sb. We infer that Yb 4 As 3 behaves as a two-fluid system with almost decoupled spin and charge excitations. Quasi-one-dimensional spin excitations within S = ½ Heisenberg chains of Yb 3− 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.