Knowledge

In response to the critique by Korolev and Talantsev regarding the calculation of the superconducting phase fraction in the Nature paper by Li et al., the authors provide a point-by-point rebuttal: first, experimental confirmation shows that the weak upturn at low temperatures originates from the background, and no paramagnetic Meissner effect is observed, validating the use of field-cooled data for calculating the superconducting phase fraction; second, the demagnetization effect must be based on the actual variation of measured magnetic moment with the superconducting phase fraction f, whereas Korolev et al. erroneously treated the demagnetizing field as a constant, causing their formula to underestimate f by approximately two-thirds (by a factor close to 1/3), which explains why their calculated result is only about one-third of the reported value (approximately 62.1%); finally, multiple characterizations of the sample (energy-dispersive X-ray spectroscopy, X-ray diffraction, nuclear quadrupole resonance, scanning transmission electron microscopy, etc.) confirm it to be a homogeneous, high-quality bulk single crystal without multiple discrete superconducting regions. Therefore, the method for calculating the superconducting phase fraction in Li et al.’s Nature paper has not been invalidated by Korolev et al.’s analysis.

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The recent discovery of a superconductivity signature in La3Ni2O7-δ under a pressure of 14 GPa, with a superconducting transition temperature of around 80 K, has attracted considerable attention. An important aspect of investigating electronic structures is discerning the extent to which the electronic ground state of La3Ni2O7-δ resembles the parent state of the cuprate superconductor, a charge transfer insulator with long-range antiferromagnetism. Through X-ray absorption spectroscopy, we reveal the influence of oxygen ligands on the electronic ground states of the Ni ions, displaying a charge transfer nature akin to cuprate but with distinct orbital configurations. Additionally, in La3Ni2O7-δ films, we detect a superlattice reflection (1/4, 1/4, L) at the Ni L absorption edge using resonant X-ray scattering measurements. Further examination of the resonance profile indicates that the reflection originates from the Ni d orbitals. By evaluating the reflection’s azimuthal angle dependence, we confirm the presence of collinear antiferromagnetic spin ordering and charge-like anisotropy ordered with the same periodicity. Our findings reveal a microscopic relationship between these two components in the temperature dependence of the scattering intensity of the reflection. This investigation enriches our understanding of high-temperature superconductivity in La3Ni2O7-δ under high pressure.

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This study employs the determinant quantum Monte Carlo method to simulate the low-energy electronic structure of infinite-layer nickelates by adding a gap s orbital with three-dimensional dispersion to the three-orbital Emery model. Large-scale calculations reveal that strong correlation effects significantly reduce the electron pocket induced by the gap s orbital, yet the pocket persists at 20% hole doping, with a size comparable to ARPES experimental observations; the d_{x^2-y^2} orbital dispersion undergoes strong renormalization, and the weak dispersion along the k_z direction agrees with experiments. Furthermore, compared to the conventional three-orbital model, the introduction of the s orbital markedly enhances short-range antiferromagnetic correlations. These results highlight the crucial role of strong correlation and multi-orbital effects in determining the low-energy electronic states and spin correlations of infinite-layer nickelates, indicating that interaction-driven many-body physics must be treated within a realistic multi-orbital framework.

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