Photocathodes—materials that convert photons into electrons using the photoelectric effect—are a critical foundation for many modern technologies that rely on light detection or electron-beam generation1,2,3. Currently existing photocathodes, however, are based on conventional metals and semiconductors that were mostly discovered six decades ago with sound theoretical underpinnings4,5. Progress in this mature field has been limited to refinements in photocathode performance based on sophisticated materials engineering1,6. Here we report unusual photoemission properties of a reconstructed surface of SrTiO3(100) single crystals prepared by simple vacuum annealing that go beyond the existing theoretical descriptions4,8,7-10. Unlike other positive-electron-affinity (PEA) photocathodes, our PEA SrTiO3 surface produces discrete secondary photoemission spectra at room temperature, characteristic of the efficient negative-electron-affinity photocathode materials11,12. At low temperatures, the photoemission peak intensity is enhanced substantially, and the electron beam obtained upon non-threshold excitations displays longitudinal and transverse coherence that shatters known records by at least an order of magnitude6,13,14. 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. SrTiO3 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.
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This file contains Supplementary Discussions 1–5, including Supplementary Figs. 1–3 and Supplementary Table 1, and the Supplementary References.
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Hong, C., Zou, W., Ran, P. et al. Anomalous intense coherent secondary photoemission from a perovskite oxide. Nature (2023). https://doi.org/10.1038/s41586-023-05900-4
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