Strain Doping: Reversible Single-Axis Control of a Complex Oxide Lattice via Helium Implantation

TL;DR

This paper demonstrates reversible, independent control of the out-of-plane lattice constant in a complex oxide thin film using helium ion implantation, enabling new ways to tune material properties beyond traditional strain methods.

Contribution

It introduces a novel helium implantation technique for reversible, single-axis lattice control in complex oxides, expanding the possibilities for material property manipulation.

Findings

Small lattice constant changes significantly alter transition temperatures.

Helium implantation allows continuous, reversible strain tuning.

The method enables independent control beyond substrate limitations.

Abstract

We report on the use of helium ion implantation to independently control the out-of-plane lattice constant in epitaxial La0.7Sr0.3MnO3 thin films without changing the in-plane lattice constants. The process is reversible by a vacuum anneal. Resistance and magnetization measurements show that even a small increase in the out-of-plane lattice constant of less than 1% can shift the metal-insulator transition and Curie temperatures by more than 100 {\deg}C. Unlike conventional epitaxy-based strain tuning methods which are constrained not only by the Poisson effect but by the limited set of available substrates, the present study shows that strain can be independently and continuously controlled along a single axis. This permits novel control over orbital populations through Jahn-Teller effects, as shown by Monte Carlo simulations on a double-exchange model. The ability to reversibly control a single lattice parameter substantially broadens the phase space for experimental exploration of predictive models and leads to new possibilities for control over materials' functional properties.