High-To superconductivity by mobilizing local spin singlets and possible route to higher To in pressurized La3Ni2O7

We clarify the pairing mechanism of high-Tc superconductivity in bilayer La3Ni2O7 under high pressure by employing the static auxiliary field Monte Carlo approach to simulate a minimal effective model that contains local d(z)(2) interlayer spin singlets and metallic d(x)(2)-y(2) bands. Superconductivity is induced when the local spin singlet pairs are mobilized and attain long-distance phase coherence by hybridization with the metallic bands. When projected onto realistic Fermi surfaces, it yields a nodeless s-wave gap on the gamma Fermi surface, and extended s-wave gaps of the same (opposite) sign on the alpha (beta) Fermi surface due to its bonding (antibonding) character, with nodes or gap minima along the diagonal direction of the two-dimensional Brillouin zone. We find a dual role of the hybridization that not only induces global phase coherence but also competes with the spin singlet formation. This lead to a tentative phase diagram where T-c varies nonmonotonically with the hybridization, in good correspondence with experimental observations. A roughly linear relation is obtained for realistic hopping and hybridization parameters: T-c approximate to 0.04-0.05J, where J is the interlayer superexchange interaction. We emphasize the peculiar tunability of the bilayer structure and propose that Tc may be further enhanced by hole doping or applying uniaxial pressure along the c axis on superconducting La3Ni2O7. Our work provides reliable numerical evidence for the pairing mechanism of high-T(c )superconductivity in La3Ni2O7 and points out a potential route to achieve even higher T-c.