Strain-controlled band engineering and self-doping in ultrathin LaNiO$_3$ films

TL;DR

This study demonstrates how strain in ultrathin LaNiO3 films induces self-doping, altering electronic properties similarly to chemical doping in bulk materials, enabling new ways to engineer electronic phases.

Contribution

It reveals strain-induced self-doping in LaNiO3 films and links it to electronic structure changes, offering a novel approach to control charge states without chemical doping.

Findings

Strain modifies transport coefficients akin to doping in cuprates.

Density functional calculations show self-doping due to strain.

Epitaxial strain can induce hole-doping in transition metal oxides.

Abstract

We report on a systematic study of the temperature-dependent Hall coefficient and thermoelectric power in ultra-thin metallic LaNiO$_3$ films that reveal a strain-induced, self-doping carrier transition that is inaccessible in the bulk. As the film strain varies from compressive to tensile at fixed composition and stoichiometry, the transport coefficients evolve in a manner strikingly similar to those of bulk hole-doped superconducting cuprates with varying doping level. Density functional calculations reveal that the strain-induced changes in the transport properties are due to self-doping in the low-energy electronic band structure. The results imply that thin-film epitaxy can serve as a new means to achieve hole-doping in other (negative) charge-transfer gap transition metal oxides without resorting to chemical substitution.