Thermal conductivity of RNi2B2C (R=Y,Ho) single crystals

We have studied the thermal conductivity κ of high-quality single crystals of YNi2B2C and HoNi2B2C. In both compounds, κ in the normal state at low temperatures is dominated by electrons. In YNi2B2C, κ shows a pronounced enhancement around 4 K well below the superconducting transition temperature Tc=15.6 K. It may be due to the increase of the phonon contribution below Tc as a result of the decrease of the number of normal electrons as scattering centers of phonons. This enhancement is suppressed largely by applying the magnetic field of Hc1 because phonons are scattered by vortices. In HoNi2B2C, κ shows a discontinuous increase at the Néel temperature TN=4.6 K and a clear decrease below Tc∼3.6 K