HEAT-CAPACITY AND THERMAL RELAXATION OF BULK HELIUM VERY NEAR THE LAMBDA-POINT

We report new high-resolution measurements of the heat capacity of liq uid helium to within 2 nK from the lambda transition, performed with a large sample in earth orbit. The optimum value for the critical expon ent characterizing the divergence of the heat capacity below the trans ition was found to be -0.01285, giving improved support for the renorm alization-group theory of phase transitions. Some information on the t emperature dependence of the thermal conductivity just above the trans ition was also obtained.