Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics & Zhejiang Institute for Advanced Light Source, Westlake University, Hangzhou, China.
UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki, Japan.
Nature. 2023 May;617(7961):493-498. doi: 10.1038/s41586-023-05900-4. Epub 2023 Mar 8.
Photocathodes-materials that convert photons into electrons through a phenomenon known as the photoelectric effect-are important for many modern technologies that rely on light detection or electron-beam generation. However, current photocathodes are based on conventional metals and semiconductors that were mostly discovered six decades ago with sound theoretical underpinnings. Progress in this field has been limited to refinements in photocathode performance based on sophisticated materials engineering. Here we report unusual photoemission properties of the reconstructed surface of single crystals of the perovskite oxide SrTiO(100), which were prepared by simple vacuum annealing. These properties are different from the existing theoretical descriptions. In contrast to other photocathodes with a positive electron affinity, our SrTiO surface produces, at room temperature, discrete secondary photoemission spectra, which are characteristic of efficient photocathode materials with a negative electron affinity. At low temperatures, the photoemission peak intensity is enhanced substantially and the electron beam obtained from non-threshold excitations shows longitudinal and transverse coherence that differs from previous results by at least an order of magnitude. The observed emergence of coherence in secondary photoemission points to the development of a previously undescribed underlying process in addition to those of the current theoretical photoemission framework. SrTiO is an example of a fundamentally new class of photocathode quantum materials that could be used for applications that require intense coherent electron beams, without the need for monochromatic excitations.
光阴极-通过光电效应将光子转化为电子的材料-对于许多依赖光探测或电子束产生的现代技术非常重要。然而，目前的光阴极基于传统的金属和半导体，这些金属和半导体大多是在六十年前基于可靠的理论基础发现的。该领域的进展仅限于基于复杂材料工程的光阴极性能的改进。在这里，我们报告了钙钛矿氧化物 SrTiO(100)单晶经简单真空退火后重构表面的异常光发射特性。这些特性与现有的理论描述不同。与具有正电子亲和力的其他光阴极不同，我们的 SrTiO 表面在室温下产生离散的二次光发射光谱，这是具有负电子亲和力的高效光阴极材料的特征。在低温下，光发射峰强度大大增强，并且从非阈值激发获得的电子束显示出与以往结果至少相差一个数量级的纵向和横向相干性。二次光发射中相干性的出现表明，除了当前的理论光发射框架之外，还出现了以前未描述的基础过程。SrTiO 是一类全新的光阴极量子材料的示例，可用于需要强相干电子束的应用，而无需单色激发。
