Transport and the order parameter of superconducting UPt₃

We calculate the ultrasonic absorption and the thermal conductivity in the superconducting state of UPt₃ as functions of temperature and direction of propagation and polarization. Two leading candidates for the superconducting order parameter are considered: the E_1g and E_2u representations. Both can fit the data except for the ultrasonic absorption in the A phase. To do that, it is necessary to suppose that the system has only a single domain, and that must be chosen as the most favorable one. However, the E_2u theory requires fine-tuning of parameters to fit the low-temperature thermal conductivity. Thus, transport data favor the E_1g theory. Measurements of the thermal conductivity as a function of pressure at low temperature could help to further distinguish the two theories.