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 <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow></mrow> <mrow> <msup><mrow><mi>z</mi></mrow> <mrow><mn>2</mn></mrow> </msup> </mrow> </msub> </math> 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.