Strong Increase of T _c of Sr ₂ RuO ₄ Under Both Tensile and Compressive Strain

Abstract

A sensitive probe of unconventional order is its response to a symmetry-breaking field. To probe the proposed p(x) ± ip(y) topological superconducting state of Sr2RuO4, we have constructed an apparatus capable of applying both compressive and tensile strains of up to 0.23%. Strains applied along ⟨100⟩ crystallographic directions yield a strong, strain-symmetric increase in the superconducting transition temperature T(c). ⟨110⟩ strains give a much weaker, mostly antisymmetric response. As well as advancing the understanding of the superconductivity of Sr2RuO4, our technique has potential applicability to a wide range of problems in solid-state physics.

Higher-Tc Superconducting Phase in Sr2RuO4 Induced by In-Plane Uniaxial Pressure

“…The [100] strain results shown in Ref. 30 at first glance appear quantitatively different from our P [100] results: it was found that T c is gradually enhanced and reaches only 1.9 K at −0.23% strain, which corresponds to 0.21 GPa stress in our experiment, according to an estimation using the elastic constants in Refs. 22 and 23.…”

“…Nevertheless, the effectiveness of P [100] in inducing the higher-T c SC phase observed in this study is clear and consistent with the results of the uniaxial strain experiments. 30 Notably, the effect of P [100] in inducing the higher-T c SC phase is greater in pure Sr 2 RuO 4 (this study) than in typical Sr 2 RuO 4 -Ru eutectic crystal (Ref. 35): for example, the diamagnetic susceptibility at 2.5 K reaches ∼ 10% at only 0.05 GPa in pure Sr 2 RuO 4 , whereas it is only 5% at 0.45 GPa in the eutectic crystal.…”

“…30 The symmetric change in T c between compressive and tensile [100] strains supports the scenario that the superconducting order parameter of Sr 2 RuO 4 has two components. The [100] strain results shown in Ref.…”

“…1, and detects the whole magnetic signal originating from the sample, whereas the pick-up coil used in Ref. 30 is much smaller than the sample and is located at the center of the sample, and thus detects the susceptibility only of the central region, which is expected to be more homogeneously strained. Thus, the superconducting signal observed in our study is dominated by regions with higher T c .…”

“…27 However, because of the technical difficulties in directly measuring the effects of in-plane UAP and uniaxial strain, the effect of in-plane UAP on Sr 2 RuO 4 has been under discussion 28,29 and the effect of in-plane uniaxial strain on Sr 2 RuO 4 has been reported only recently. 30 In this study, we have investigated the AC susceptibility of Sr 2 RuO 4 under in-plane UAP along two directions, [100] or [110], to obtain hints for determining the SC order parameter of Sr 2 RuO 4 , whose orbital part is expected to have two components under ambient conditions.…”