Electron correlations and superconductivity in <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> under pressure tuning
Zhiguang Liao, Lei Chen, Guijing Duan, Yiming Wang, Changle Liu, Rong Yu, Qimiao Si
Abstract
Motivated by the recent discovery of superconductivity in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ under pressure, we discuss the basic ingredients of a model that captures its microscopic physics under pressure tuning. We anchor our description in terms of the spectroscopic evidence of strong correlations in this system. In a bilayer Hubbard model including the Ni $3d$ ${x}^{2}\ensuremath{-}{y}^{2}$ and ${z}^{2}$ orbitals, we show the ground state of the model crosses over from a low-spin $S=1/2$ state to a high-spin $S=3/2$ state. In the high-spin state, the two ${x}^{2}\ensuremath{-}{y}^{2}$ and the bonding ${z}^{2}$ orbitals are all close to half-filling, which promotes a strong orbital selectivity in a broad crossover regime of the phase diagram pertinent to the system. Based on these results, we construct an effective multiorbital $t\text{\ensuremath{-}}J$ model to describe the superconductivity of the system, and find the leading pairing channel to be an intraorbital spin singlet with a competition between the extended $s$-wave and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ symmetries. Our results highlight the role of strong multiorbital correlation effects in driving the superconductivity of ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$.