“Quantum Avalanche” – A Phenomenon That May Revolutionize Microelectronics and Supercomputing
International Conference on Nuclear Physics
New Study Solves Mystery on Insulator-to-Metal Transition
A study explored insulator-to-metal transitions, uncovering discrepancies in the traditional Landau-Zener formula and offering new insights into resistive switching. By using computer simulations, the research highlights the quantum mechanics involved and suggests that electronic and thermal switching can arise simultaneously, with potential applications in microelectronics and neuromorphic computing
Looking only at their subatomic particles, most materials can be placed into one of two categories.
Metals — like copper and iron — have free-flowing electrons that allow them to conduct electricity, while insulators — like glass and rubber — keep their electrons tightly bound and therefore do not conduct electricity.
Insulators can turn into metals when hit with an intense electric field, offering tantalizing possibilities for microelectronics and supercomputing, but the physics behind this phenomenon called resistive switching is not well understood.
The Mystery of Insulator-to-Metal Transitions
Questions, like how large an electric field is needed, are fiercely debated by scientists, like University at Buffalo condensed matter theorist Jong Han.
“I have been obsessed by that,” he says.
Metals — like copper and iron — have free-flowing electrons that allow them to conduct electricity, while insulators — like glass and rubber — keep their electrons tightly bound and therefore do not conduct electricity.
Insulators can turn into metals when hit with an intense electric field, offering tantalizing possibilities for microelectronics and supercomputing, but the physics behind this phenomenon called resistive switching is not well understood.
The Mystery of Insulator-to-Metal Transitions
Questions, like how large an electric field is needed, are fiercely debated by scientists, like University at Buffalo condensed matter theorist Jong Han.
“I have been obsessed by that,” he says.
Electrons Move Through Quantum Paths
The difference between metals and insulators lies in quantum mechanical principles, which dictate that electrons are quantum particles and their energy levels come in bands that have forbidden gaps, Han says.
Since the 1930s, the Landau-Zener formula has served as a blueprint for determining the size of electric field needed to push an insulator’s electrons from its lower bands to its upper bands. But experiments in the decades since have shown materials require a much smaller electric field — approximately 1,000 times smaller — than the Landau-Zener formula estimated.
Solving Discrepancies
To solve this, Han decided to consider a different question: What happens when electrons already in the upper band of an insulator are pushed?
Han ran a computer simulation of resistive switching that accounted for the presence of electrons in the upper band. It showed that a relatively small electric field could trigger a collapse of the gap between the lower and upper bands, creating a quantum path for the electrons to go up and down between the bands.
To make an analogy, Han says, “Imagine some electrons are moving on a second floor. When the floor is tilted by an electric field, electrons not only begin to move but previously forbidden quantum transitions open up and the very stability of the floor abruptly falls apart, making the electrons on different floors flow up and down.
“Then, the question is no longer how the electrons on the bottom floor jump up, but the stability of higher floors under an electric field.”
This idea helps solve some of the discrepancies in the Landau-Zener formula, Han says. It also provides some clarity to the debate over insulator-to-metal transitions caused by electrons themselves or those caused by extreme heat. Han’s simulation suggests the quantum avalanche is not triggered by heat. However, the full insulator-to-metal transition doesn’t happen until the separate temperatures of the electrons and phonons — quantum vibrations of the crystal’s atoms — equilibrate. This shows that the mechanisms for electronic and thermal switching are not exclusive of each other, Han says, but can instead arise simultaneously.
Research Could Improve Microelectronics
The study was co-authored by Jonathan Bird, PhD, professor and chair of electrical engineering in UB’s School of Engineering and Applied Sciences, who provided experimental context. His team has been studying the electrical properties of emergent nanomaterials that exhibit novel states at low temperatures, which can teach researchers a lot about the complex physics that govern electrical behavior.
“While our studies are focused on resolving fundamental questions about the physics of new materials, the electrical phenomena that we reveal in these materials could ultimately provide the basis of new microelectronic technologies, such as compact memories for use in data-intensive applications like artificial intelligence,” Bird says.
Potential Applications
The research could also be crucial for areas like neuromorphic computing, which tries to emulate the electrical stimulation of the human nervous system. “Our focus, however, is primarily on understanding the fundamental phenomenology,” Bird says.
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