Heat Capacity and Thermal Relaxation of Bulk Helium very near the Lambda Point

We report new high-resolution measurements of the heat capacity of liquid helium to within 2 nK from the lambda transition, performed with a large sample in earth orbit. The optimum value for the critical exponent characterizing the divergence of the heat capacity below the transition was found to be $-0.01285\mathrm{}$, giving improved support for the renormalization-group theory of phase transitions. Some information on the temperature dependence of the thermal conductivity just above the transition was also obtained.