The microscopic mechanism of Cooper pairing in a superconductor leaves its fingerprint on the symmetry of the order parameter. UTe2 has been inferred to have a multi-component order parameter that entails exotic effects like time reversal symmetry breaking. However, recent experimental observations in newer-generation samples have raised questions about this interpretation, pointing to the need for a direct experimental probe of the order parameter symmetry. Here, we use pulse-echo ultrasound to measure the elastic moduli of UTe2 in samples that exhibit both one and two superconducting transitions. We demonstrate the absence of thermodynamic discontinuities in the shear elastic moduli of both single- and double-transition samples, providing direct evidence that UTe2 has a single-component superconducting order parameter. We further show that superconductivity is highly sensitive to compression strain along the a and c axes, but insensitive to strain along the b axis. This leads us to suggest a single-component, odd-parity order parameter -- specifically the B2u order parameter -- as most compatible with our data.
@article{arxiv.2307.10938,
title = {Single-Component Superconductivity in UTe$_2$ at Ambient Pressure},
author = {Florian Theuss and Avi Shragai and Gael Grissonnanche and Ian M Hayes and Shanta R Saha and Yun Suk Eo and Alonso Suarez and Tatsuya Shishidou and Nicholas P Butch and Johnpierre Paglione and B. J. Ramshaw},
journal= {arXiv preprint arXiv:2307.10938},
year = {2024}
}