We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound ${\mathrm{CeIrIn}}_5$ as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature $T^{*}$ that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce $4f$ states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.

• Received 4 July 2014

DOI:https://doi.org/10.1103/PhysRevB.92.085108