Possible counterintuitive enhancement of superconductivity in ladder-type cuprates by longitudinal compression

We explore how the electron hoppings of the ladder type cuprates are affected when uniaxial compression or tension is applied to the lattice in the leg or rung directions, and investigate its consequences to superconductivity. For simplicity, we consider the two-leg ladder cuprate without the chains, that is, SrCu₂O₃, although this material is known to be difficult to dope carriers. By constructing a model based on first principles calculation, we surprisingly find that the ratio t_r/t_l, where t_r(t_l) is the nearest neighbor hopping in the rung (leg) direction, is enhanced when the lattice is compressed in the leg direction or stretched in the rung direction. This counterintuitive manner of the hopping variation can be attributed to the on-site hybridization between Cu d_x²−y² and Cu 4s orbitals, which arises due to the low symmetry of the lattice. We apply the fluctuation exchange approximation to the model and study how superconductivity is affected under uniaxial deformation. Due to the above mentioned variation of the hoppings, we find that the superconducting transition temperature is enhanced when the lattice is compressed in the leg direction, opposed to an intuitive expectation. The effect is expected to be strong especially in the electron-doped regime.