We present thermal-conductivity and thermopower S measurements on high-quality single crystalline CeNiSn along the three crystallographic axes a, b, and c in the temperature range between 100 mK and 7 K and in magnetic fields up to 8 T applied along the a axis. Both and S are highly anisotropic. However, characteristic features that may be attributed to the opening of a pseudogap in the electronic density of states ͑DOS͒ at the Fermi energy below 10 K are seen for all three crystallographic directions. These features are strongly suppressed by a magnetic field of 8 T applied along the a axis. At the lowest temperatures we have evidence for the presence of a residual metallic DOS at , again for all three directions. The saturation of the reduced Lorenz number L/L 0 to a value distinctly higher than one is an interesting feature which deserves further investigation.

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We report low-temperature measurements of the specific heat, thermal expansion, and thermal conductivity on the quasi-one-dimensional, effective S 1 2 Heisenberg antiferromagnet Yb 4 As 3 . Distinct field-induced anomalies were found in the above quantities which are well described by the classical sine-Gordon soliton solution for an easy-plane Heisenberg antiferromagnet. Our findings strongly suggest that Yb 4 As 3 represents the first example of an antiferromagnetic S 1 2 spin-chain system where this type of nonlinear excitation could be identified. [S0031-9007 (99)09295-9] PACS numbers: 75.30.Mb, 05.45.Yv, 65.50. + m, 65.70. + y

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