Angle-resolved photoemission spectroscopy of superconducting (La,Pr)3Ni2O7/SrLaAlO4 heterostructures

TL;DR

This study uses ARPES to investigate the electronic structure of ultrathin (La,Pr)3Ni2O7/SrLaAlO4 heterostructures, revealing interface-localized conduction, hole doping, and orbital contributions relevant to understanding nickelate superconductivity.

Contribution

First ARPES study of ultrathin nickelate heterostructures showing interface confinement, orbital contributions, and doping effects, advancing understanding of their superconducting mechanisms.

Findings

Conduction localized at the first unit cell near the interface.

Evidence of hole doping compared to bulk crystals.

Both Ni dx2-y2 and dz2 orbitals contribute at the Fermi level.

Abstract

Ruddlesden-Popper bilayer nickelate thin film superconductors discovered under ambient pressure enable vast possibilities for investigating electronic structures of the superconducting state. Here, we report angle-resolved photoemission spectroscopy (ARPES) measurements of 1, 2, and 3 unit-cell epitaxial La2.85Pr0.15Ni2O7 films grown on SrLaAlO4 substates, through pure-oxygen in situ sample transportation. Evidence obtained using photons with distinct probing depths shows that conduction is localized primarily at the first unit cell near the interface. Scanning transmission electron microscopy (STEM), together with energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), indicates that interfacial Sr diffusion and pronounced p-d hybridization gradient may collectively account for the interfacial confinement of conduction. Fermi surface maps reveal hole doping compared to non-superconducting ambient-pressure bulk crystals. Measurements of dispersive band structures suggest the contributions from both Ni dx2-y2 and dz2 orbitals at the Fermi level. Density functional theory (DFT) + U calculations capture qualitative features of the ARPES results, consistent with a hole-doped scenario. These findings constrain theoretical models of the superconducting mechanism and suggest potential for enhancing superconductivity in nickelates under ambient pressure.