Colossal magnetocapacitance and scale-invariant dielectric response in phase-separated manganites

TL;DR

This paper introduces a novel experimental technique using a MIM capacitor structure to measure out-of-plane dielectric responses in thin film manganites, revealing scale-invariant behavior and distinct insulator-metal transitions.

Contribution

The study presents an innovative method to simultaneously measure perpendicular dielectric and in-plane transport properties in strongly-correlated electron materials.

Findings

Observation of colossal magnetocapacitance in the out-of-plane direction.

Identification of two strain-related insulator-metal transitions.

Universal scale-invariant power-law dielectric response across various conditions.

Abstract

Thin films of strongly-correlated electron materials (SCEM) are often grown epitaxially on planar substrates and typically have anisotropic properties that are usually not captured by edge-mounted four-terminal electrical measurements, which are primarily sensitive to in-plane conduction paths. Accordingly, the correlated interactions in the out-of-plane (perpendicular) direction cannot be measured but only inferred. We address this shortcoming and show here an experimental technique in which the SCEM under study, in our case a 600 Angstrom-thick (La1-yPry)0.67Ca0.33MnO3 (LPCMO) film, serves as the base electrode in a metal-insulator-metal (MIM) trilayer capacitor structure. This unconventional arrangement allows for simultaneous determination of colossal magnetoresistance (CMR) associated with dc transport parallel to the film substrate and colossal magnetocapacitance (CMC) associated with ac transport in the perpendicular direction. We distinguish two distinct strain-related direction-dependent insulator-metal (IM) transitions and use Cole-Cole plots to establish a heretofore unobserved collapse of the dielectric response onto a universal scale-invariant power-law dependence over a large range of frequency, temperature and magnetic field.