High-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>T</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> superconductivity by mobilizing local spin singlets and possible route to higher <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>T</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:math> in pressurized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Ni</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math>
Qiong Qin, Yi‐feng Yang
Abstract
We clarify the pairing mechanism of high-${T}_{c}$ superconductivity in bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ 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 ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ 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 $\ensuremath{\gamma}$ Fermi surface, and extended $s$-wave gaps of the same (opposite) sign on the $\ensuremath{\alpha}$ ($\ensuremath{\beta}$) 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 leads 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: ${T}_{c}\ensuremath{\approx}0.04\ensuremath{-}0.05J$, where $J$ is the interlayer superexchange interaction. We emphasize the peculiar tunability of the bilayer structure and propose that ${T}_{c}$ may be further enhanced by hole doping or applying uniaxial pressure along the $c$ axis on superconducting ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. Our work provides reliable numerical evidence for the pairing mechanism of high-${T}_{c}$ superconductivity in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ and points out a potential route to achieve even higher ${T}_{c}$.