A Chinese-led team of scientists claimed to have achieved a breakthrough that could rewrite Albert Einstein’s Nobel Prize-winning theory.
In 1905, Einstein published a paper explaining the photoelectric effect, in which he put forth that light comprises discrete packets, “energy quanta,” now called ‘photons,’ as opposed to the wave theory of light, which was widely accepted at the time.
He predicted that photons above a certain threshold frequency when falling on a specific material, eject electrons from its surface. This phenomenon is called the photoelectric effect, which is said to have resulted in the 20th-century quantum revolution in physics.
The discovery of the photoelectric effect earned Einstein the 1921 Nobel Prize in Physics.
The discovery of the photoelectric effect laid the foundation for several modern-day technologies that depend on light detection or electron-beam generation.
High-energy electron beams have been used at a large scale to analyze crystal structures, treat cancer, kill bacteria, and machine alloy.
The materials that convert photons into electrons are known as photocathodes. Notably, most of the photocathodes known today were discovered around 60 years ago, and all of them are said to have a defect.
The electrons these photocathodes generate are dispersed in angle and speed.
After over a century after Einstein received the 1921 Nobel Prize for the discovery of the photoelectric effect, a team of researchers from China, Japan, and the US has now published a paper that, according to reports, could cause the new quantum revolution.
Strontium Titanate (SrTiO3)
A team of researchers led by He Ruihua, of Westlake University in Hangzhou, in China’s eastern Zhejiang province, published a paper in the peer-reviewed journal Nature on March 8.
In this paper, the team used a new material called strontium titanate (SrTiO3) to acquire a concentrated beam of electrons with a level of energy enhanced by at least an order of magnitude.
Strontium titanate (SrTiO3) is a quantum material with a diverse set of interesting properties. According to He’s team, electron beams obtained after exciting SrTiO3 are coherent.
“Coherence is important to the beam, it concentrates the flow like a pipe on the tap. Without the pipe, water will spray everywhere when the tap is wide open. Without coherence, electrons will scatter,” said Hong Caiyun, an author of the paper.
“With the coherence we acquired, we can increase the beam intensity while the beam could maintain its direction,” Hong further said.
Also, the intensity of photoemission from SrTiO3 is greatly enhanced, according to the team.
“This exceptional performance suggests novel physics beyond the well-established theoretical framework for photoemission,” Hong said.
Addition To Einstein’s Original Discovery
The discovery has driven the team to find a new theory to explain unparalleled coherence.
“We came up with an explanation as a supplement to Einstein’s original theoretical framework. It’s in another paper which is under review right now,” Professor He said.
Co-author of the paper Arun Bansil of Northeastern University in the US has hailed the discovery.
“This is a big deal because there is no mechanism within our existing understanding of photoemission that can produce such an effect. In other words, we don’t have any theory for this, currently, so it is a miraculous breakthrough in that sense,” Bansil said.
According to Hong, the new theory predicts the existence of an entire class of materials with the same photoemissive properties as SrTiO3.
“SrTiO3 presents the first example of a fundamentally new class of photocathode quantum materials. It opens new prospects for applications that require intense electron beams,” she said.
Professor He said the discovery came from their focus on a traditional technology called angle-resolved photoemission spectroscopy (ARPES).
ARPES is widely used to study electron structures in solid materials, usually crystalline solids. It measures the kinetic energy and emission angle distributions of the emitted photoelectrons.
“In the past few decades, physics and material scientists mainly used ARPES to study the electronic structures related to the optical, electrical, and thermal properties. Our team adapted an unconventional configuration of ARPES and measured another part that’s more related to the photoelectric effect,” He said.
“During the test, we found the unusual photoemission properties of SrTiO3. Previously, quantum oxide materials represented by strontium titanate were mainly studied as substitutes for semiconductors and are currently used in the fields of electronics and photocatalysis.
“The material will definitely be promising in the field of photocathode in the future.”
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