The claim that a single electron absorbs only one photon in the photoelectric effect is a foundational principle of quantum mechanics (Albert Einstein's light quanta explanation), so basic and well-established that it requires no citation.
The claim states a fundamental, textbook tenet of quantum physics regarding the photoelectric effect established by Einstein in 1905. The retrieved papers discuss unrelated advanced topics such as multi-photon absorption, single-photon sources, and optical metrology, rather than contesting this core principle. Per instructions, fundamental definitions and textbook physical principles of this kind are categorized as COMMON_KNOWLEDGE.