When a current is applied to a thin layer of tungsten diselenide, it begins to glow in a highly unusual fashion. In addition to ordinary light, which other semiconductor materials can emit, tungsten diselenide also produces a very special type of bright quantum light, which is created only at specific points of the material. It consists of a series of photons that are always emitted one by one—never in pairs or in bunches. This anti-bunching effect is perfect for experiments in the field of quantum information and quantum cryptography, where single photons are required. However, for years, this emission has remained a mystery.
Source:
https://phys.org/news/2019-10-mystery-quantum-thin-layers.html