So far superlattice devices, which represent an essential part of modern electronics and optics, relied on complicated fabrication of artificial multilayers. This work presents the first experimental evidence for resonant stimulated emission, bearing some resemblance with operation of a superlattice-based Quantum Cascade Laser. However, the phenomenon occurs not in the artificial superlattice, but in a piece of a naturally grown layered single crystal. The material studied is the high temperature superconductor Bi_2 Sr_2 CaCu_2 O_8+x , in which mobile charge carriers are confined to CuO_2 planes. This leads to formation of a natural “intrinsic” superlattice at the atomic scale. Yet, the mechanism of the observed phenomenon is very unusual and, despite certain similarities, is conceptually different from emission in the Quantum Cascade Laser. For example, the band gap is not due to level quantization in a superlattice but is the superconducting energy gap; and stimulated emission appears when bosonic (rather than electronic) bans overlap. It is argued that the observed phenomenon may reveal the coupling mechanism of high temperature superconductors and demonstrates a possibility of employing natural atomic superlattices for building electronic devices at the ultimate atomic scale.
See also press release: http://www.forskning.se/servlet/GetDoc?meta_id=90795&templat