Room-Temperature Terahertz Photoconductivity Polarity Switching in High Entropy Nickelates with Implications for Photonic Synapses

TL;DR

This study demonstrates room-temperature THz photoconductivity polarity switching in high entropy nickelates, revealing phase transitions and coexistence of photoconductivity types, with implications for developing advanced photonic synapses and high-speed THz applications.

Contribution

It introduces a novel methodology combining high entropy rare earth nickelates and epitaxial strain to manipulate phase behavior and photoconductivity at THz frequencies, supported by theoretical modeling.

Findings

Room-temperature THz insulator-metal phase transition dependent on crystal axis

Coexistence of negative and positive THz photoconductivity at room temperature

Disproportionate oxygen vacancy ordering as the origin of observed properties

Abstract

High entropy oxides (HEO) hold the potential to revolutionize the conventional material paradigms by leveraging high order of chemical disorder that induces highly desirable exotic phases for advanced applications. Here, we devise a methodology to enhance the efficiency of an artificial photonic synapse using a high entropy rare earth nickelate. Combined with epitaxial strain, we show that high entropy can further manipulate the phase of these locally disordered materials. Using time-averaged and time resolved Terahertz (THz) spectroscopy as dynamic probe, for the first time we show a rare combination of i) crystal axis dependent insulator to metal THz electronic phase transition and ii) coexistence of negative and positive THz photoconductivity at room temperature. Detailed analysis within theoretical models, including density functional theory (DFT)-based band structure calculations, suggest origin of these properties as disproportionate ordering of oxygen vacancies. Based on these findings, a conceptual THz-based artificial photonic synapse is proposed. This work underlines the pivotal role of HEO in advancing diverse THz functionalities, representing a critical step toward futuristic applications like THz-based high-speed computing and communication with an emphasis in THz frequency domain.