A world first! Chinese scientists have discovered the “quantum” material of the light cathode

The reporter learned from Westlake University that the research group of He Ruihua of the School of Science of Westlake University, together with research collaborators, discovered the world’s first photocathode quantum material with intrinsic coherence, whose performance far exceeds that of traditional photocathode materials, and cannot be explained by existing theories, opening up a new world for the development, application and basic theory development of photocathodes.

In the early morning of March 9, Beijing time, the related paper “Anomaly Strong Coherent Secondary Photoelectron Emission on a Perovskite Oxide” has been published online in the journal Nature in advance. 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, Westlake University, is the corresponding author.


Under the photographer’s lens, the first photocathode quantum material with intrinsic coherence: strontium titanate.

In 1887, German physicist Hertz accidentally discovered in experiments that ultraviolet rays irradiating electrodes on metal surfaces would produce sparks. In 1905, Einstein proposed a theoretical explanation of the phenomenon based on the quantization conjecture of light. This marks the official opening of the door to quantum mechanics. As a result, the “photoelectric effect” that converts “light” into “electricity”, and the “photocathode” material that can produce this effect, officially entered the field of vision of mankind.

“These photocathode materials are basically traditional metal and semiconductor materials, most of which were discovered 60 years ago. They have become the core components of cutting-edge technological devices such as contemporary particle accelerators, free-electron lasers, ultrafast electron microscopy, and high-resolution electron spectrometers. However, these traditional materials have inherent performance shortcomings – the electron beams they emit are too “coherent” to be too coherent, that is, the emission angle of the electron beam is too large, and the electrons in them move at different 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.


The difference between the initial electron beam emitted by the ordinary photocathode material (a) and the photocathode quantum material strontium titanate (b).

Although electrode-based electron gun technology has developed greatly in recent decades, it has gradually been unable to keep pace with the development 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 from the School of Science of Westlake University, which is deeply engaged in the research of the physical properties of materials, accidentally achieved a breakthrough in a quantum material “common” in similar physics laboratories – strontium titanate.

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.

Zheng Changxi, an ultrafast electron microscopy expert, paper co-author and researcher at the School of Science at Westlake University, believes that the importance of the team’s discovery is not to add 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.

The reporter learned that next, the team will carry out further research on related materials in terms of theory and application.

(All pictures from Westlake University)
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