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Revealing isotropic abundant low-energy excitations in UTe2 through complex microwave surface impedance

Arthur Carlton-Jones1, Alonso Suarez1, Yun-Suk Eo2, Ian M. Hayes1, Shanta R. Saha1, Johnpierre Paglione1,3, Nicholas P. Butch1,4, and Steven M. Anlage1

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Phys. Rev. B 112, 014519 – Published 24 July, 2025

DOI: https://doi.org/10.1103/t2w3-z3j3

Abstract

The complex surface impedance is a well-established tool to study the super- and normal-fluid responses of superconductors. Fundamental properties of the superconductor, such as the pairing mechanism, Fermi surface, and topological properties, also influence the surface impedance. We explore the microwave surface impedance of spin-triplet UTe2 single crystals as a function of temperature using resonant cavity perturbation measurements employing a multimodal analysis to gain insight into these properties. We determine a composite surface impedance of the crystal for each mode using resonance data combined with the independently measured normal state dc resistivity tensor. The normal state surface impedance reveals the weighting of current flow directions in the crystal of each resonant mode. For UTe2, we find an isotropic Δλ(T)∼Tα power-law temperature dependence for the magnetic penetration depth for T≤Tc/3 with α<2, which is inconsistent with a single pair of point nodes on the Fermi surface under weak scattering. We also find a similar power-law temperature dependence for the low-temperature surface resistance Rs(T)∼TαR with αR<2. We observe a strong anisotropy of the residual microwave loss across these modes, with some modes showing loss below the universal line-nodal value, to those showing substantially more. We compare to predictions for topological Weyl superconductivity in the context of the observed isotropic power laws and anisotropy of the residual loss.

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Phys. Rev. B 112, 014519– Published 24 July, 2025
  • Received 11 February 2025
  • Revised 26 May 2025
  • Accepted 25 June 2025
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