Comprehensive model of anomalous intense coherent secondary photoemission from an oxide semiconductor

The recent discovery of an anomalous intense and coherent secondary photoemission signal from 2x1 surface reconstructed SrTiO₃¹ has several perplexing aspects that evade explanation from the conventional theoretical framework of secondary photoemission. We present a comprehensive model which can coherently explain all the puzzling features of the experiment including the presence of a second energy dependent threshold in addition to the typical photoemission threshold, the dramatic orders of magnitude increase in intensity upon decreasing temperature, and the coexistence of monochromaticity alongside high quantum efficiency within a positive electron affinity material. This model is based on a novel point of view which includes the components of Auger recombination and flat electronic bands. Furthermore, as a future test of our model we show that it predicts below photoemission threshold emission under specific conditions. Finally, guided by the salient features proposed to make the 2x1 reconstructed SrTiO₃ exceptional, we identify a diverse set of other materials which are predicted to exhibit the same anomalous behavior.

1. Hong, C. et al. Anomalous intense coherent secondary photoemission from a perovskite oxide. Nature 617, 493-498 (2023).