Photocathodes are a critical foundation for many modern technologies that rely on light detection or electron-beam generation. Currently existing photocathodes, however, are based on conventional metals and semiconductors that were mostly discovered six decades ago with sound theoretical underpinnings. Progress in this mature field has been limited to refinements in photocathode performance based on sophisticated materials engineering.

Recently, Ruihua He's team at Westlake University discovered the first photocathode quantum material: a reconstructed surface of strontium titanate single crystals. The electron beam they obtained upon non-threshold excitations of the material displays longitudinal and transverse coherence that shatters known records by at least an order of magnitude. The observed emergence of coherence in secondary photoemission points to the development of an underlying novel process on top of those encompassed in the current theoretical photoemission framework. Strontium titanate thus presents the first example of a fundamentally new class of photocathode quantum materials, opening new prospects for applications that require intense coherent electron beams without the need for monochromatic excitations, electron filtering or beam acceleration.

The research results were published in Nature in a piece called ‘Anomalous intense coherent secondary photoemission from a perovskite oxide’, which can be read here: https://doi.org/10.1038/s41586-023-05900-4

Figure 1. The difference between the electron beams emitted from conventional materials (a) and the photocathode quantum material strontium titanate (b)