An electrically pumped polariton laser

An electrically pumped polariton laser is constructed using a quantum well microcavity, and its polaritonic nature is demonstrated unambiguously by using a magnetic field to probe the part-light, part-matter character of the system. An energy-efficient electrical polariton laser Polariton lasers have the potential to be more energy efficient than conventional semiconductor lasers that depend on coherent light (photon) beams. When light and electronic excitations hybridize in an optical cavity, part-light part-matter exciton–polaritons are created, and these can emit coherent light without the population inversion required in conventional lasers. Optically pumped polariton lasers have been demonstrated previously but it has been an outstanding goal to produce one that is electrically operated, an essential step towards practical applicability. Sven Höfling and colleagues have now achieved that. Importantly they provide unambiguous proof that the laser emission they observe has a hybrid light–matter nature. Conventional semiconductor laser emission relies on stimulated emission of photons 1 , 2 , which sets stringent requirements on the minimum amount of energy necessary for its operation 3 , 4 . In comparison, exciton–polaritons in strongly coupled quantum well microcavities 5 can undergo stimulated scattering that promises more energy-efficient generation of coherent light by ‘polariton lasers’ 3 , 6 . Polariton laser operation has been demonstrated in optically pumped semiconductor microcavities at temperatures up to room temperature 7 , 8 , 9 , 10 , 11 , 12 , and such lasers can outperform their weak-coupling counterparts in that they have a lower threshold density 12 , 13 . Even though polariton diodes have been realized 14 , 15 , 16 , electrically pumped polariton laser operation, which is essential for practical applications, has not been achieved until now. Here we present an electrically pumped polariton laser based on a microcavity containing multiple quantum wells. To prove polariton laser emission unambiguously, we apply a magnetic field and probe the hybrid light–matter nature of the polaritons. Our results represent an important step towards the practical implementation of polaritonic light sources and electrically injected condensates, and can be extended to room-temperature operation using wide-bandgap materials.