Strong peak in the critical temperature of Sr2RuO4 induced by strain tuning

Orateur : Clifford HICKS (Max Planck Institute for Chemical Physics of Solids, Dresden, Germany)

We use piezoelectric-based uniaxial pressure apparatus to apply in situ-tunable orthorhombic distortions to the tetragonal, layered perovs kite compounds Sr2RuO4 and Sr3Ru2O7. Sr3Ru2O7 has an anomalous phase associated with proximity to a metamagnetic quantum critical endpoint, that responds strongly to C2-symmetric fields. This phase has been found to host (100)- and (010)-oriented spin density waves, and orthorhombic distortion appears to continuously lift their degeneracy, in a manner more consistent with microscopic coexistence than spontaneous symmetry breaking. Lifting the tetragonal symmetry of Sr2RuO4 was expected to similarly lift the degeneracy of the px and py components of its proposed px±ipy superconducting order parameter. Whether this happens or not is still under investigation ; what is clearly observed is that with strong orthorhombic distortion, Tc more than doubles and passes through a well-defined peak. The upper critical field Hc2 is very strongly enhanced at this peak. Implications for the symmetry of the order parameter will be discussed.

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