Gigantic Anisotropic Uniaxial Pressure Effect on Superconductivity within the CuO₂ Plane of La_1.64Eu_0.2Sr_0.16CuO₄: Strain Control of Stripe Criticality

Abstract

The effect of uniaxial pressure on superconductivity was examined for high-T_c cuprate La_1.64Eu_0.2Sr_0.16CuO₄, which is located at the boundary between the superconducting and stripe phases. We found markedly large anisotropy of the uniaxial pressure effect not only between the in-plane and out-of-plane pressures but also within the tetragonal CuO₂ plane. When the pressure is applied along the [110] direction, we found the largest pressure effect ever observed in cuprates, dT_c⁄dP_[110]∼2.5 K/kbar, while the change in T_c was not appreciable when the pressure is applied along [100]. This substantial in-plane anisotropy is attributed to an intimate link between the symmetry of one-dimensional stripes and that of the strain produced within the CuO₂ plane.