Abstract
We report on the first measurement of the anisotropy of heat conduction in a heavy fermion superconductor, performed on a single crystal of U with a current parallel and perpendicular to the hexagonal axis. Beyond the temperature-independent anisotropy of the normal state, a clear additional anisotropy develops in the superconducting state. This direct measure of gap anisotropy places precise constraints on the possible states for the two zero-field phases. An axial gap is excluded for both, and a comparison with existing calculations favors a -wave gap for the low-temperature phase.
- Received 18 July 1994
DOI:https://doi.org/10.1103/PhysRevLett.73.3294
©1994 American Physical Society