Imagine a computer that can think like a human and use very little energy. Scientists want to discover or develop materials that can send and process signals as easily as the brain. Identifying quantum materials with an ability to switch between two different forms may hold the key to these futuristic sounding computing technologies.
Yimei Zhu, a physicist at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, and his colleagues describe new details about vanadium dioxide in a paper published in the journal Physical Review X. The team captured the hidden trajectory of atomic motion as this material transitions from an insulator to a metal in response to a pulse of light. Their findings could help guide the design of high-speed and energy-efficient devices.
The main idea behind this energy efficiency is that quantum materials have non- linear properties.
He said thatvanadium dioxide is one of the rare, amazing materials that has emerged as a promising candidate for bio-inspired devices. It exhibits a transition near room temperature in which a small voltage or current can produce a large change in resistivity with a switch that can mimic the behavior of both neurons and synapses.
It goes from a very good rubber conductor to a very good metal conductor with a change of 10,000 times or more.
There are two very different physical states in the same material.
Ultrafast atomic motions are visualized.
The scientists used short particles of light for their experiments. They captured the material's atomic-scale response using the MeV-UED instrument.
This tool is similar to a camera that has a shutter left open in a dark setting, firing intermittent flashes to catch a thrown ball in motion. The camera records an image with each flash, and the series of images taken at different times shows the ball's trajectory in flight.
The MeV-UEDstroboscope captures the dynamics of a moving object in a similar way, but at a much faster time scale. It uses high-energy electrons.
Junjie Li, the first author of the paper, said that previous static measurements only revealed the initial and final state of the vanadium dioxide-to-metal transition.
The whole story is not told by the pictures alone. The scientists used sophisticated time-resolved crystallographic analysis techniques to refine the intensity changes of a few dozen electron diffraction peaks.
The instrument has an energy of 3 MeV, which is 50 times higher than smaller laboratory-based ultrafast electron microscopes.
Two stage dynamics and a path.
The second stage of the transition is longer in duration and slower in speed than the first, according to the analysis. The motions of the atoms in the second stage were not linear.
The shortest possible distance from position A to B would be a direct straight line. It was a curve. This was completely unforeseen.
The curve shows that there is more than one force involved in the transition.
Think back to the stroboscopic images of a ball. You exert force when you throw a ball. The trajectory to curve is caused by gravity pulling the ball to the ground.
The force that gets the transition going is the light pulse, and the force that causes the atomic trajectory to change is the electrons around the vanadium atoms.
The study showed that a measure related to the intensity of light used to cause atomic dynamics can affect the trajectory of a ball. The ball or the atoms can overcome the competing interaction if the force is large enough.
To confirm and understand the atomic dynamics, the team carried out density functional theory calculations. They were able to see the cumulative effects of forces on the structures and provide snapshots of the atomic motions.
The paper describes how the combination of theory and experimental studies provided detailed information, including how the vanadium atoms stretch and rotation over time during the transition. The research addressed some long-standing scientific questions about vanadium dioxide, including the existence of an intermediate phase during the insulator-to-metal transition, the role of photoexcitation-induced thermal heating, and the origin of incomplete transitions under photoexcitation.
The study sheds new light on how photo-induced electronic and lattice dynamics affect this particular phase transition and should help push the evolution of computing technology.
We still have a long way to go, but I think we are on the right track, when it comes to making a computer that mimics the human brain.
More information: Junjie Li et al, Direct Detection of V-V Atom Dimerization and Rotation Dynamic Pathways upon Ultrafast Photoexcitation in VO2, Physical Review X (2022). DOI: 10.1103/PhysRevX.12.021032 Journal information: Physical Review X Citation: Ultrafast 'camera' captures hidden behavior of potential 'neuromorphic' material (2022, May 9) retrieved 9 May 2022 from https://phys.org/news/2022-05-ultrafast-camera-captures-hidden-behavior.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
All Rights Reserved © 2024
