Anomalous heat capacity of spin triplet superconductor UTe2

The recently discovered superconducting state in uranium ditelluride is a playground of exotic phenomena, including field-reentrant superconductivity up to sixty tesla and spin-triplet pairing.[1, 2] In addition this system shows a large residual density of states at zero temperature, suggesting that about half of the electrons fail to condense, and an apparent violation of entropy balance across the superconducting transition.[1, 3] This talk will present milikelvin specific heat data on UTe2 as a function of magnetic field applied along multiple crystallographic axes. The specific heat shows an upturn at the lowest temperatures. The form of the upturn in temperature and its evolution in magnetic field suggest that it has its origin in critical ferromagnetic fluctuations, supporting the idea that UTe2 is the paramagnetic end member of the series of uranium-based ferromagnetic superconductors. Furthermore, subtracting this upturn restores entropy balance to the superconducting transition. The talk will conclude with a discussion of the implications of these observations for the triplet pairing scenario.

S. Ran et al, Science 365 684 (2019)
S Ran et al, arxiv:1905:04343 (2019)
T. Metz et al, arXiv:1908.01069 (2019)