Superconductivity in the Hubbard model with next-nearest-neighbor hopping
In plain words
Adding a small diagonal hopping t', as in real cuprates, appears to tilt the balance toward superconductivity when electrons are removed.
Precise statement
For the square-lattice $t-t'-U$ Hubbard model with $t'/t \sim -0.2\ \text{to}\ -0.3$ and $U/t = 8$, determine the ground-state phase diagram versus hole and electron doping in the thermodynamic limit: presence, magnitude and symmetry of the superconducting order parameter and its coexistence with partially filled stripes or Neel order. An answer is a phase diagram with extrapolated order parameters and an estimate of $T_c/t$.
What would settle it
Thermodynamic-limit extrapolations from DMRG on wide cylinders, AFQMC and tensor networks that agree on the phase boundaries and order-parameter magnitudes.
Status in the literature
Unverified note
DMRG and AFQMC (2024) found d-wave order coexisting with partially filled stripes on the hole-doped side and with Neel order on the electron-doped side.