Evidence for magnons and solitons in the one-dimensional S=1/2 antiferromagnet Yb4As3

By means or low-temperature measurements of the specific heat. C. and therm al expansion. alpha = l(-1) partial derivative l/partial derivative T, the magnetic properties of the quasi-one-dimensional (quasi-1D). S = 1/2 Heisen berg antiferromagnet Yb4As3 were investigated. In finite magnetic fields di stinct anomalies were found which are pronounced differently strongly in bo th quantities: (i) the in-T linear contribution dominating the low-T specif ic heat becomes reduced with field and (ii) a peak is induced at slightly h igher temperatures. The latter feature being much more pronounced in alpha( T, B) is well described by the classical sine-Gordon (SG) soliton solution of a 1D Heisenberg antiferromagnet with a weak easy-plane anisotropy. (C) 2 000 Elsevier Science B.V. All rights reserved.