Excitations in spill chains and specific-heat anomalies in Yb(4)AS(3)

An explanation is given for the observed magnetic-field dependence of the low-temperature specific-heat coefficient of Yb4As3. It is based on a recently developed model for that material which can explain the observed heavy-fermion behaviour. According to it, the Yb3+ ions are positioned in a net of parallel chains with an effective spin coupling of the order of J approximate to 25 K. The magnetic-field dependence can be understood by including a weak magnetic coupling J' between adjacent chains. The data require a ratio J'/J approximate to 10(-4). In that case the experimental results can be reproduced very well by the theory.