surface impedance through microwave resonance measurements*

The complex surface impedance of a superconductor provides many insights into its properties, such as the pairing mechanism, super- and normal-fluid responses, and possibly it’s topological properties. We explore the surface impedance of UTe₂ single crystals as a function of temperature using resonant cavity measurements for a variety of microwave-frequency modes. By determining the resonant frequency and quality factor over a range of temperatures, we reconstruct the surface impedance of the sample.  We match the behavior of the resistance and reactance in the normal state to their expected behavior, determined by the normal state resistivity.  Since UTe₂ is anisotropic, we take a linear combination of the losses corresponding to each crystallographic direction to do this fitting.  Through this method, the anisotropic nature of UTe₂ allows us to determine the combination of crystallographic directions excited in each resonant mode.  We present the results of the anisotropic surface impedance temperature dependence in the superconducting and normal states, and relate the results to topics of current interest in this unique material.