Uniaxial strain, topological band singularities and pairing symmetry changes in superconductors

Uniaxial strain affects pairing symmetry states in superconductors by changing the lattice symmetry, and by altering Fermi surface topology. Here, we present a systematic study of these effects
within a one-band negative-U Hubbard model for s, p and d-wave pairing states. We consider a
general 2D model that can be applied to superconductors under uniaxial strain, modelled via hopping anisotropy, on a square lattice. The results presented here model an in plane compression
along the x-axis, which reduces the lattice symmetry from a tetragonal to an orthorhombic crystal
space group. The effects of hopping anisotropy on the different types of gap pairings are explored.
We show that changes in Tc are tunable with hopping anisotropy and depend on the orientation of
the gap function in relation to the opening of the Fermi surface during the Lifshitz transition. In
comparing the model results to experimental data for the case of Sr2RuO4 it is found that both the
d + id and d + ig pairings best describe the changes in Tc for the superconducting state in regards
to its response to small uniaxial strain.