Scientists discovered the world’s first photocathode quantum material

He Ruihua’s research group in the School of Science of Westlake University, together with research collaborators, discovered the world’s first photocathode quantum material with intrinsic coherence, which far exceeds the traditional photocathode material and cannot be explained by existing theories, opening up a new world for the development, application and basic theoretical development of photocathodes.

Under the photographer’s lens, the first photocathode quantum material with intrinsic coherence: strontium titanate. Photo courtesy of the research group

On March 9, the relevant research results were published online in Nature under the title “Anomaly Strong Coherent Secondary Photoelectron Emission on a Perovskite Oxide”. Hong Caiyun, Zou Wenjun and Ran Pengxu, doctoral students of Westlake University, are the co-first authors of the paper, and He Ruihua, tenured associate professor of the School of Science of Westlake University, is the corresponding author of the paper.

Photocathode materials are the core components of contemporary particle accelerators, free electron lasers, ultrafast electron microscopy, high-resolution electron spectrometers and other cutting-edge scientific and technological devices. It has always had inherent performance flaws – the emitted electron beam is too “coherent”, that is, the emission angle of the electron beam is too large, and the electrons in it move at uneven speeds. In order to meet the requirements of cutting-edge technological applications, such an “initial” electron beam must rely on a series of material processes and electrical engineering techniques to enhance its coherence, and the introduction of these special processes and auxiliary technologies greatly increases the complexity of the “electron gun” system, increasing construction requirements and costs.

Although the electron gun technology based on the time cathode has developed greatly in recent decades, it has gradually been unable to keep up with the pace of related technological applications. Many of the above-mentioned cutting-edge technology upgrades call for an order of magnitude improvement in the coherence of the initial electron beam, which is no longer possible with general photocathode performance optimization, and can only hope for source innovation at the material and theoretical level.

He Ruihua’s team accidentally achieved a breakthrough in a quantum material “strontium titanate (SrTiO3)”, which is “common” in a physics laboratory.

Previous research on oxide quantum materials led by strontium titanate was mainly to study these materials as potential alternatives to silicon-based semiconductors, but He Ruihua’s team unexpectedly captured these familiar materials through a powerful but rarely applied experimental method in photocathode research: angle-resolved photoelectron spectroscopy technology, which also carries the ability to trigger novel photoelectric effects – it has far more than the key performance of photocathodes of existing photocathode materials: coherence, and cannot be explained by existing photoelectric emission theory.

An anonymous reviewer of the Nature paper noted: “This discovery may lead to a paradigm shift in photocathode technology, which has long been trapped by the contradiction that the electron beam cannot have high coherence and high beam intensity at the same time, and the root cause of this contradiction lies in the intrinsic incoherence of the initial electron beam.” ”

Zheng Changxi, a co-author and researcher at Westlake University’s School of Science, believes that the importance of the team’s discovery “lies not in adding a new property to the list of magical properties of strontium titanate, but in the property itself, which may restart an extremely important field of time-cathode technology that is widely regarded as mature, changing many long-ingrained rules of the game.” (Source: Wen Caifei, China Science News)

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