Pseudogap of metallic layered nickelate R2-xSrxNiO4 (R=Nd, Eu) crystals measured using angle-resolved photoemission spectroscopy

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal a pseudogap in layered nickelates, suggesting charge correlations as its origin, similar to underdoped cuprates despite weaker magnetic interactions.

Contribution

First demonstration of a pseudogap in layered nickelates and its association with charge correlations using ARPES.

Findings

Large hole surface with x2-y2 character observed

Pseudogap of similar symmetry and magnitude to underdoped cuprates

Pseudogap likely arises from real-space charge correlations

Abstract

We have investigated charge dynamics and electronic structures for single crystals of metallic layered nickelates, R2-xSrxNiO4 (R=Nd, Eu), isostructural to La2-xSrxCuO4. Angle-resolved photoemission spectroscopy on the barely-metallic Eu0.9Sr1.1NiO4 (R=Eu, x=1.1) has revealed a large hole surface of x2-y2 character with a high-energy pseudogap of the same symmetry and comparable magnitude with those of underdoped (x<0.1) cuprates, although the antiferromagnetic interactions are one order of magnitude smaller. This finding strongly indicates that the momentum-dependent pseudogap feature in the layered nickelate arises from the real-space charge correlation.