Source capture
Authors Zhiming Pan, Chen Lu, Fan Yang, Congjun Wu
arXiv / Publisher http://arxiv.org/abs/2604.20613v1
PDF https://arxiv.org/pdf/2604.20613v1
Relevance score 5.387
Primary category Not available in this batch.
Published Not available in this batch.
Research paradigm Theoretical
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Summary

The high-temperature superconductivity in bilayer La3Ni2O7 originates from its unique two-orbital bilayer electronic structure, where the 3d_z2 orbital is nearly half-filled and localized, generating strong interlayer antiferromagnetic exchange via the inner apical oxygen 2p_z orbital, while the 3dx2-y2 orbital is approximately quarter-filled and highly itinerant. Under strong coupling, Hund’s rule coupling aligns the spins of the two orbitals on the same nickel site, effectively transferring the interlayer antiferromagnetic exchange to the itinerant 3dx2-y2 orbital, forming an effective coupling J⊥. This mechanism can be simplified into a strong-coupling bilayer t-J-J⊥ model for the 3dx2-y2 band, where J⊥ drives electrons to form interlayer Cooper pairs, realizing extended s-wave pairing superconductivity with high critical temperature. Meanwhile, the strongly localized 3d_z2 electrons tend to form interlayer ladder singlets; due to the lack of phase coherence, these singlets do not directly participate in the superconducting condensation but instead give rise to a pseudogap phase. This review systematically elaborates on this strong-coupling Hund’s rule assisted pairing theory, providing a unified framework for understanding the mechanism of high-temperature superconductivity in this system.

Materials

Methods

Keywords

Highlights

  • A strict division of labor between orbitals: d_z2 acts as magnetic glue, dx2-y2 hosts mobile Cooper pairs.
  • Electron doping is predicted to enhance Tc, providing a testable route.

Conclusions

  • Hund's rule coupling aligns spins of localized d_z2 and itinerant dx2-y2 orbitals, transferring interlayer antiferromagnetic exchange to the dx2-y2 band, resulting in extended s-wave pairing with high Tc.
  • The d_z2 orbital forms interlayer rung singlets that yield a pseudogap phase but do not directly contribute to superconductivity.

Main claims

  • The 3d_z2 orbital is nearly half-filled and localized, generating strong interlayer antiferromagnetic exchange via the inner apical oxygen 2p_z orbital.
    • Evidence: the 3d_z2 orbital is nearly half-filled and localized, generating strong interlayer antiferromagnetic exchange via the inner apical oxygen 2p_z orbital
  • Hund's rule coupling aligns the spins of the two orbitals on the same nickel site, effectively transferring the interlayer antiferromagnetic exchange to the itinerant 3dx2-y2 orbital, forming an effective coupling J⊥.
    • Evidence: Under strong coupling, Hund’s rule coupling aligns the spins of the two orbitals on the same nickel site, effectively transferring the interlayer antiferromagnetic exchange to the itinerant 3dx2-y2 orbital, forming an effective coupling J⊥.
  • This mechanism can be simplified into a strong-coupling bilayer t-J-J⊥ model for the 3dx2-y2 band, which realizes extended s-wave pairing superconductivity with high Tc.
    • Evidence: This mechanism can be simplified into a strong-coupling bilayer t-J-J⊥ model for the 3dx2-y2 band, where J⊥ drives electrons to form interlayer Cooper pairs, realizing extended s-wave pairing superconductivity with high critical temperature.

Workflow

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