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Uniaxial strain study of Sr2RuO4

The unconventional superconductor Sr 2 RuO 4 has been proposed to support a time-reversal symmetry breaking, spin triplet vector order parameter of the form d = z Δ o ( p x + ip y ).  If correct, this would be a 2D analogue of the A phase of superfluid 3 He, and would imply topological superconductivity with edge states and unconventional vortices supporting Majorana fermions.  However, the evidence to date is inconclusive, with some but not all the characteristic signatures of such a state having been observed.  Since the order parameter involves two degenerate spatial states, uniaxial strain is an ideal way to probe it, because the strain should break the degeneracy by imposing a preferred direction.  Novel home-built uniaxial strain apparatus has allowed us to apply both compressive and tensile strains of up to 0.25%, and to apply strain along the (100) and (110) crystallographic directions.  I will discuss the results and their implications for our understanding of the superconductivity of Sr 2 RuO 4 , and briefly review the possibilities that the new technique opens for work on other materials.