The microscopic mechanism of Cooper pairing in a superconductor leaves its fingerprint on the symmetry of the order parameter. UTe₂ has previously been inferred to have a multi-component order parameter, in part due to the apparent presence of a two-step superconducting transition in some samples. However, recent experimental observations in newer-generation samples have raised questions about this interpretation, pointing to the need for a direct 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 B_2u order parameter—as most compatible with our data.

超导体中库珀配对的微观机制在有序参数的对称性上留下了痕迹。 UTe ₂先前被推断具有多组分有序参数，部分原因是某些样品中明显存在两步超导转变。然而，最近对新一代样本的实验观察对这种解释提出了质疑，指出需要直接探测有序参数对称性。在这里，我们使用脉冲回波超声来测量同时表现出一次和两次超导转变的样品中UTe ₂的弹性模量。我们证明了单转变和双转变样品的剪切弹性模量不存在热力学不连续性，提供了 UTe ₂具有单组分超导有序参数的直接证据。我们进一步表明，超导性对沿a和c轴的压缩应变高度敏感，但对沿b轴的应变不敏感。这导致我们建议使用单分量奇宇称序参数（特别是B _{2 u}序参数），因为它与我们的数据最兼容。