Upper critical field of Sr₂RuO₄ under uniaxial stress

Through application of in-plane uniaxial stress, the unconventional superconductor Sr₂RuO₄ can be driven through a Lifshitz transition and associated Van Hove singularity (VHS) in the density of states. At this point, its Tc is enhanced by a factor of about 2.5, and H_c2 by about twenty. Here, we present data on H_c2 at intermediate strains, and observe that the peak in H_c2 is much sharper than that in T_c. The ratio H_c2/T_c² increases in the close vicinity to the VHS, providing information on the evolution of the superconducting gap as the VHS is approached.

[1] C.W. Hicks et al. Science 344.6181 (2014): 283-285.
[2] A. Steppke et al., Science 355, eaaf9398 (2017)