Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe2 remains elusive. This puzzle stems from reports of either a single or a double superconducting transition at ambient pressure as well as a complex pressure-temperature phase diagram. To address this issue, we measured the heat capacity and electrical resistivity of UTe2 under compressive uniaxial stress σ applied along different crystallographic directions. We find that the critical temperature Tc of the single observed bulk superconducting transition decreases with σ along  and  but increases with σ along . Aside from its effect on Tc, c-axis stress leads to a significant piezoresistivity. Importantly, an in-plane shear stress σxy does not induce any observable splitting of the superconducting transition over a stress range of σxy≈0.17GPa. This result suggests that the superconducting order parameter of UTe2 may be single component at ambient pressure.
Bibliographical noteFunding Information:
The LANL LDRD program supported the development of ac calorimetry under uniaxial stress. The remaining experimental work and crystal synthesis at LANL were supported by the U.S. DOE, Office of Basic Energy Sciences project “Quantum Fluctuations in Narrow Band Systems.” J.X.Z. (DFT calculations) was supported by the Quantum Science Center and in part by CINT, in partnership with the LANL Institutional Computing Program. C.S. and A.H. (crystal synthesis) were supported by U.K. EPSRC Grant No. EP/P013686/1. R.M.F. (phenomenological modeling) was supported by the U.S. DOE, Office of Basic Energy Sciences, Award No. DE-SC0020045.
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