Excitations in Spin 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 Yb(4)As(3). It is based on a recently developed model for that material which can explain the observed heavy-fermion behaviour. According to it the Yb(3+)-ions are positioned in a net of parallel chains with an effective spin coupling of the order of J = 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 of about 10^{-4}. In that case the experimental results can be reproduced very well by the theory. 
Burkhard Schmidt, Peter Thalmeier, and Peter Fulde   (Max-Planck-Institute for Physics of Complex Systems)