Probing the evolution of electronic phase-coexistence in complex systems by terahertz radiation

TL;DR

This paper introduces a novel terahertz spectroscopy method combined with DC transport to investigate electronic phase-coexistence in complex oxides, revealing disparities in phase transition signatures at different frequencies.

Contribution

It demonstrates a new approach using THz spectroscopy to probe electronic inhomogeneities and phase coexistence, offering insights into phase transition mechanisms in complex materials.

Findings

THz conductivity remains insulating at low temperatures despite DC metallic behavior.

The disparity in responses is due to the different sensitivities to cluster sizes.

Methodology is broadly applicable to study phase coexistence in various materials.

Abstract

In complex oxides, the electrons under the influence of competing energetics are the cornerstone of coexistence (or phase-separation) of two or more electronic/magnetic phases in same structural configuration. Probing of growth and evolution of such phase-coexistence state is crucial to determine the correct mechanism of related phase-transition. Here, we demonstrate the combination of terahertz (THz) time-domain spectroscopy and DC transport as a novel strategy to probe the electronic phase-coexistence. This is demonstrated in disorder controlled phase-separated rare-earth nickelate thin films which exhibit metal-insulator transition in dc conductivity at around 180 K but lack this transition in terahertz (THz) dynamics conductivity down to low temperature. Such pronounced disparity exploits two extreme attributes: i) enormous sensitivity of THz radiation to a spatial range of its wavelength-compatible electronic inhomogeneities and ii) insensitivity to a range beyond the size of its wavelength. This feature is generic in nature (sans a photo-induced effect), depends solely on the size of insulating/metallic clusters and formulates a methodology with unique sensitivity to investigate electronic phase-coexistence and phase transition of any material system.