Abstract
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 B2u order parameter—as most compatible with our data.
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Data availability
Data that support the plots within this paper and other findings of this study are available via GitHub at https://github.com/CHiLL-Ramshaw/manuscripts-supporting_data/tree/0292ab9b15b60af93341e64b759507e4e59eb7cd/2024_Single_Component_Superconductivity_in_UTe2_at_Ambient_Pressure (ref. 44) and from the corresponding author upon reasonable request. Source data are provided with this paper.
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Acknowledgements
We acknowledge helpful discussions with D. Agterberg and P. Brydon. We thank the Cornell LASSP Professional Machine Shop for their contributions to designing and fabricating equipment used in this study. A. Shragai, B.J.R. and F.T. acknowledge funding from the Office of Basic Energy Sciences of the United States Department of Energy under award number DE-SC0020143 (ultrasound experiments and analysis). N.P.B. and J.P. acknowledge support from the Department of Energy award number DE-SC-0019154 (sample characterization), the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant number GBMF9071 (materials synthesis), the National Science Foundation under grant number DMR-2105191 (sample preparation) and the Maryland Quantum Materials Center and the National Institute of Standards and Technology. B.J.R. and F.T. acknowledge use of the Cornell Center for Materials Research Shared Facilities which are supported through the NSF MRSEC programme (DMR-1719875). G.G. acknowledges support from the ANR grants STeP2 no ANR-22-EXES-0013 and QuantEx no ANR-23-CE30-0001-01.
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Contributions
B.J.R. conceived the experiment. I.M.H., S.R.S., Y.S.E. and A. Suarez grew and characterized the samples. F.T. and A. Shragai performed the sample preparation and transducer fabrication. F.T., A. Shragai and G.G. performed the ultrasound measurements. F.T. and B.J.R. performed the data analysis and mean-field calculations. T.S. performed density functional theory calculations. F.T. and B.J.R. wrote the paper with input from all other co-authors. J.P., N.P.B. and B.J.R. supervised the project.
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Extended data
Extended Data Fig. 1 Raw Pulse-Echo Signal.
The raw signal from a sputtered ZnO shear transducer on sample S3 with sound propagation along the [010] and polarization along the [100] directions. The transducer exhibits both a compressional (blue lines) and a shear (red dashed lines) response. These correspond to sound modes determined by the elastic moduli c22 and c66, respectively.
Extended Data Fig. 2 Comparison of different transducers.
Shown are Δc33/c33 for single Tc (S1, left) and two Tc (S3, right) samples. For each sample we compare the relative change in elastic modulus between measurements obtained with two different transducers. Both transducers excited sound along the [001] direction. However, for the data in red, the shear component of the transducer was polarized along [100] (additionally measuring c55), whereas for the data in blue, the shear component of the transducer was polarized along [010] (additionally measuring c44).
Supplementary information
Supplementary Information
Supplementary Figs. 1–11, Discussion and Tables 1–3.
Source data
Source Data Fig. 2
Delta c/c for samples with one superconducting transition.
Source Data Fig. 3
Delta c/c for samples with one and two superconducting transitions.
Source Data Fig. 4
Delta c/c for compressional elastic moduli.
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Theuss, F., Shragai, A., Grissonnanche, G. et al. Single-component superconductivity in UTe2 at ambient pressure. Nat. Phys. (2024). https://doi.org/10.1038/s41567-024-02493-1
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DOI: https://doi.org/10.1038/s41567-024-02493-1
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