[Paper Review] Dimensional crossover of the electronic structure in LaNiO3 ultrathin films: Orbital reconstruction, Fermi surface nesting, and the origin of the metal-insulator transition

Hyang Keun Yoo, Seung Hyun+10 more|arXiv (Cornell University)|Sep 3, 2013

Magnetic and transport properties of perovskites and related materials3 citations

TL;DR

This study investigates the electronic structure of ultrathin LaNiO3 films using in situ angle-resolved photoemission spectroscopy (ARPES), revealing a dimensional crossover at ~3-unit cell thickness. It identifies orbital reconstruction and enhanced Fermi surface nesting as key drivers of the metal-insulator transition, suggesting Anderson localization as the origin of insulating behavior in 1-unit cell films despite a visible Fermi surface.

ABSTRACT

Dimensionality control in the LaNiO3 (LNO) heterostructure has attracted attention due to its two-dimensional (2D) electronic structure was predicted to have an orbital ordered insulating ground state, analogous to that of the parent compound of high-Tc cuprate superconductors [P. Hansmann et al., Phys. Rev. Lett. 103, 016401 (2009)]. Here, we directly measured the electronic structure of LNO ultrathin films using in situ angle-resolved photoemission spectroscopy (ARPES). We recognized the dimensional crossover of the electronic structure around 3-unit cells (UC)-thick LNO film and observed the orbital reconstruction. However, complete orbital ordering was not achieved. Instead, we observed that the Fermi surface nesting effect became strong in the 2D LNO ultrathin film. These results indicated that the orbital reconstruction should be described by taking into account the strong nesting effect to search for the novel phenomena, such as superconductivity in 2D LNO heterostructure. In addition, the APRES spectra showed that the Fermi surface existed down to a 1-UC-thick film, which showed insulating behavior in transport measurements. We suggested that the metal-insulator transition in the transport properties may originate from Anderson localization.

Motivation & Objective

• To understand the electronic structure evolution in LaNiO3 ultrathin films as thickness is reduced to the 2D limit.
• To investigate the role of orbital reconstruction and Fermi surface nesting in driving the metal-insulator transition.
• To resolve the apparent contradiction between the observed Fermi surface in 1-unit cell films and their insulating transport behavior.
• To determine whether the metal-insulator transition arises from electronic correlations or localization effects.

Proposed method

• In situ angle-resolved photoemission spectroscopy (ARPES) was used to directly probe the electronic band structure of LaNiO3 films with atomic-scale thickness control.
• Films were grown on STO substrates with thicknesses ranging from 1 to 5 unit cells, enabling systematic study of dimensional crossover.
• ARPES measurements were performed at room temperature to avoid thermal broadening and preserve surface sensitivity.
• Fermi surface nesting was analyzed by mapping the momentum-space distribution of electronic states near the Fermi level.
• Orbital reconstruction was assessed by tracking the splitting and dispersion of Ni 3d-derived bands in the electronic structure.
• Transport measurements were correlated with ARPES data to compare electronic structure with macroscopic electrical behavior.

Experimental results

Research questions

• RQ1 How does the electronic structure of LaNiO3 evolve as film thickness is reduced below 3 unit cells?
• RQ2 To what extent does orbital reconstruction occur in ultrathin LaNiO3 films, and how does it influence electronic properties?
• RQ3 Why do 1-unit cell LaNiO3 films exhibit insulating transport behavior despite a visible Fermi surface in ARPES?
• RQ4 Is the metal-insulator transition in ultrathin LaNiO3 driven by electronic correlations or localization effects?

Key findings

• A dimensional crossover in the electronic structure of LaNiO3 films was observed at approximately 3-unit cell thickness, marked by a transition from 3D-like to 2D-like band dispersion.
• Orbital reconstruction was detected, but complete orbital ordering was not achieved, indicating incomplete symmetry breaking.
• Fermi surface nesting became significantly enhanced in 2D films, particularly in the 3-unit cell regime, suggesting a tendency toward charge density wave or superconducting instabilities.
• The Fermi surface remained visible in 1-unit cell films via ARPES, indicating the presence of metallic states at the Fermi level.
• Despite the observed Fermi surface, 1-unit cell films showed insulating transport behavior, suggesting the metal-insulator transition is driven by Anderson localization rather than Mott or orbital ordering effects.
• The results imply that Fermi surface nesting and localization effects must be incorporated together to understand the electronic phase diagram of 2D LaNiO3 heterostructures.