Orbital-dependent electron correlation in double-layer nickelate La3Ni2O7

Abstract

The latest discovery of high temperature superconductivity near 80 K in La3Ni2O7 under high pressure has attracted much attention. Many proposals are put forth to understand the origin of superconductivity. The determination of electronic structures is a prerequisite to establish theories to understand superconductivity in nickelates but is still lacking. Here we report our direct measurement of the electronic structures of La3Ni2O7 by high-resolution angle-resolved photoemission spectroscopy. The Fermi surface and band structures of La3Ni2O7 are observed and compared with the band structure calculations. Strong electron correlations are revealed which are orbital- and momentum-dependent. A flat band is formed from the Ni-3d$${}_{{z}^{2}}$$ z 2 orbitals around the zone corner which is ~ 50 meV below the Fermi level and exhibits the strongest electron correlation. In many theoretical proposals, this band is expected to play the dominant role in generating superconductivity in La3Ni2O7. Our observations provide key experimental information to understand the electronic structure and origin of high temperature superconductivity in La3Ni2O7.

The Quest for High-Temperature Superconductivity in Nickelates under Ambient Pressure

“…One possibility is that this is related to the known DFT's inability to adequately describe the ground state of strongly correlated electron materials, of which nickelates and cuprates are prime examples-e.g., DFT predicts La 2 CuO 4 to be metallic, while, experimentally, it is an antiferromagnetic insulator. In nickelates, some relevant electron energy bands near the Fermi level are strongly renormalized; the DFT bands are as much as 500-800% wider than the bands measured by ARPES experiments [26][27][28]. Rhodes and Wahl have argued that the chemistry and crystal structure are usually controlled by the electron spectrum and states at higher (few eV) energy scales and that DFT adequately describes these [18].…”

Normal and Superconducting Properties of La3Ni2O7

“…Therefore, Hall effect measurements indicate that the electronic behavior of the 𝑑 𝑧 2 orbitals may be localized, and the conductivity is primarily contributed by the 𝑑 𝑥 2 −𝑦 2 orbital, roughly consistent with the ARPES experiment at ambient pressure. [54] When the temperature is lowered for the as-prepared sample, the Hall coefficient 𝑅H gets enhanced below about 120 K, showing the signature of a density wave gap near Fermi energy. As the oxygen content decreases to 𝛿 ≥ 0.08, the Hall coefficient increases about five times, which is not accountable by a simple counting of the nominal hole number (0.5-𝛿)/Ni.…”

“…In the 2222 structure, the 𝛼 and 𝛽 bands display relatively mild band renormalizations, approximately 2, which are nearly isotropic in momentum space, similar to those observed in La4Ni3O10. [54,59] In contrast, the 𝛾 band in the same structure undergoes…”

“…The electronic band structures of La3Ni2O7 in two distinct structures, 2222 and 1313, have been investigated using ARPES. [54,56] Figure 7 displays these measurements alongside results from DFT calculations. In both structures, three primary bands are identified near the Fermi level: the Ni-3𝑑 𝑥 2 −𝑦 2 -derived 𝛼 and 𝛽 bands, and the Ni-3𝑑 𝑧 2 -derived 𝛾 band, consistent with DFT predictions.…”

“…ing temperature could be used to elucidate the mechanisms driving this energy gap in La3Ni2O7. [54,56] In the trilayer nickelate La4Ni3O10, the density-wave transition results in an intertwined state exhibiting both charge and spin order below TDW. [68] This difference between La4Ni3O10 and La3Ni2O7 was confirmed by an ultrafast reflectivity measurement.…”