Pairing without $γ$-Pocket in the La$_3$Ni$_2$O$_7$ Thin Film
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| Format: | Preprint |
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2025
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| _version_ | 1866918105386582016 |
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| author | Shao, Zhi-Yan Lu, Chen Liu, Min Liu, Yu-Bo Pan, Zhiming Wu, Congjun Yang, Fan |
| author_facet | Shao, Zhi-Yan Lu, Chen Liu, Min Liu, Yu-Bo Pan, Zhiming Wu, Congjun Yang, Fan |
| contents | The recent discovery of high-temperature superconductivity (HTSC) in the La$_3$Ni$_2$O$_7$ ultrathin film at ambient pressure has aroused great research interest. The $γ$-pocket formed by the bonding $d_{z^2}$ band, which was previously proposed to be crucial in the pairing mechanism of pressurized bulk La$_3$Ni$_2$O$_7$, is reported to be either present or absent here by different experimental groups, giving rise to the problem: what is the pairing mechanism and pairing nature without the $γ$-pocket? Here, we start from a band structure obtained via density-functional-theoretical calculation, which exhibits no $γ$-pocket. Then, equipped with electron interactions, we study the pairing nature via combined weak- and strong- coupling approaches, which provide consistent results. In the weak-coupling study, the nesting between the $α$- and $β$- pockets leads to an $s^\pm$-wave pairing in which the gap signs on the two pockets are opposite, as provided by our random-phase-approximation based calculations. In real-space, the pairing pattern is dominated by the interlayer pairing of the $d_{x^2-y^2}$ orbital. In the strong-coupling study, as the $d_{z^2}$ orbitals are nearly half-filled and hence localized, the $d_{x^2-y^2}$ orbitals carry the HTSC. Driven by the interlayer superexchange transferred from the $d_{z^2}$ orbital through the Hund's rule coupling, the $d_{x^2-y^2}$ orbital electrons form interlayer $s$-wave pairing, as suggested by our slave-boson-mean-field study on the related two-orbital $t$-$J$ model. Projected onto the Fermi surface, this pairing just gives the $s^\pm$-wave pattern consistent with that obtained in the weak-coupling study. Our result is consistent with that obtained in recent scanning tunneling microscopy experiment. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_20287 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Pairing without $γ$-Pocket in the La$_3$Ni$_2$O$_7$ Thin Film Shao, Zhi-Yan Lu, Chen Liu, Min Liu, Yu-Bo Pan, Zhiming Wu, Congjun Yang, Fan Superconductivity Strongly Correlated Electrons The recent discovery of high-temperature superconductivity (HTSC) in the La$_3$Ni$_2$O$_7$ ultrathin film at ambient pressure has aroused great research interest. The $γ$-pocket formed by the bonding $d_{z^2}$ band, which was previously proposed to be crucial in the pairing mechanism of pressurized bulk La$_3$Ni$_2$O$_7$, is reported to be either present or absent here by different experimental groups, giving rise to the problem: what is the pairing mechanism and pairing nature without the $γ$-pocket? Here, we start from a band structure obtained via density-functional-theoretical calculation, which exhibits no $γ$-pocket. Then, equipped with electron interactions, we study the pairing nature via combined weak- and strong- coupling approaches, which provide consistent results. In the weak-coupling study, the nesting between the $α$- and $β$- pockets leads to an $s^\pm$-wave pairing in which the gap signs on the two pockets are opposite, as provided by our random-phase-approximation based calculations. In real-space, the pairing pattern is dominated by the interlayer pairing of the $d_{x^2-y^2}$ orbital. In the strong-coupling study, as the $d_{z^2}$ orbitals are nearly half-filled and hence localized, the $d_{x^2-y^2}$ orbitals carry the HTSC. Driven by the interlayer superexchange transferred from the $d_{z^2}$ orbital through the Hund's rule coupling, the $d_{x^2-y^2}$ orbital electrons form interlayer $s$-wave pairing, as suggested by our slave-boson-mean-field study on the related two-orbital $t$-$J$ model. Projected onto the Fermi surface, this pairing just gives the $s^\pm$-wave pattern consistent with that obtained in the weak-coupling study. Our result is consistent with that obtained in recent scanning tunneling microscopy experiment. |
| title | Pairing without $γ$-Pocket in the La$_3$Ni$_2$O$_7$ Thin Film |
| topic | Superconductivity Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2507.20287 |