Publications by Steve Simon

Strong peak in Tc of Sr2RuO4 under uniaxial pressure

Science American Association for the Advancement of Science 355 (2016) eaaf9398

H Rosner, T Scaffidi, F Jerzembek, AS Gibbs, Y Maeno, ME Barber, AP Mackenzie, CW Hicks, SH Simon, A Stepke, L Zhao

We report a combined experimental and theoretical study of the dependence of the superconductivity of the unconventional superconductor Sr2RuO4 on anisotropic strain. Novel piezoelectric apparatus is used to apply uniaxial pressures of up to ∼1 GPa along a h100i direction (a-axis) of the crystal lattice. Tc increases from 1.5 K in unstrained material to 3.4 K at compression by ≈0.6%, then falls steeply. The c-axis upper critical field for the strained Tc = 3.4 K material is a factor of twenty larger than that of the unstrained crystal, whereas the in-plane (a-axis) critical field increases by only a factor of three. First-principles electronic structure calculations give evidence that the observed maximum Tc occurs at or near a Lifshitz transition when the Fermi level passes through a van Hove singularity. Finally, we perform order parameter analyses using three-band renormalization group calculations. These, combined with the unexpectedly low in-plane critical field, open the possibility that the highly strained Tc=3.4 K Sr2RuO4 has an even- rather than an odd-parity order parameter. Potential implications such as a transition at nonzero strain between odd- and even-parity order parameters are discussed.

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