Digital- to Analog-Type Terahertz Modulation Controlled by Mosaicity of the Substrate Template in Rare-Earth Nickelate Thin Films

Abstract

The extreme sensitivity of the metal–insulator (M–I) transition in RNiO3 (R = rare-earth ion) nickelates to various extrinsic and intrinsic factors rely on mechanisms driving structure–property relations. Here, we demonstrate a unique way to control the M–I transition of epitaxial Pr0.5Sm0.5NiO3 thin films using a mosaic template of the LaAlO3(100) substrate; two sets of epitaxial films were deposited on highly oriented crystals and mosaic (with multiple crystallites) crystals. While the former films exhibit a robust and sharp M–I transition, the films on the mosaic substrate show distinctively much more subtle and broad transition, albeit same factors suggesting compositional purity. Terahertz (THz) dynamic conductivity too behaves very differently for the two types of films; Drude dynamics dominate the conductivity of highly crystalline films, whereas disorder-driven Drude–Smith conductivity prevails in mosaic films. Using this mosaic structure-controlled M–I transition and conductivity dynamics, we propose to implement these two templates of films for digital and analog THz transmission amplitude modulators.

Terahertz Phase Shift and Its Modulation in NdGaO3 Single Crystals

“…Oxide crystals are widely utilized not only as functional materials but also as film substrates in optical devices because of their fruitful optical properties, high temperature resistance, corrosion resistance, low expansion coefficient, and high chemical stability. − In this work, four typical oxide crystals, i.e., SiO 2 , Al 2 O 3 , LSAT, and NGO, were selected as representative materials for the THz phase modulation studies. The temperature dependence of the THz transmission of four oxide crystals are explored at first and the typical results are shown in Figure .…”

Terahertz Electrodynamics in Transition Metal Oxides

“…Optical Mater. [220][221][222][223][224][225] Phase diagram of rare-earth nickelates as a function of tolerance factor or rare-earth ionic radius.…”

“…Such behavior is extensively studied and demonstrated using THz-TDS in LaNiO 3 , La 0.5 Eu 0.5 NiO 3 , and PrNiO 3 thin films. [220][221][222][223][224][225]…”

Active and Smart Terahertz Electro-Optic Modulator Based on VO2 Structure

“…To create high-performance THz modulators, especially the active and smart ones, appropriate materials with tunable optical and electric properties are indispensable. In addition to the intensively studied doped semiconductors, − two-dimensional (2D) materials, , and liquid crystals, strongly correlated electron oxides such as vanadium oxides , and rare earth nickelates, , in which their exotic properties governed by electron-electron interaction, have also drawn much attention. Among them, vanadium dioxide (VO 2 ) is a prototype due to its reversible near-room-temperature (∼340 K) insulator-to-metal transition (IMT).…”