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Loughborough University Institutional Repository Electron locking in semiconductor superlattices

We describe a novel state of electrons and phonons arising in semiconductor superlattices (SSL) due to strong electron-phonon interactions. These states are characterized by a localization of phonons and a self-trapping or locking of electrons in one or several quantum wells due to additional, deformational potential arising around these locking wells in SSL. The effect is enhanced in a longitudinal magnetic field. Using the tight-binding and adiabatic approximations the whole energy spectrum of the self-trapped states is found and accurate, analytic expressions are included for strong electron-phonon coupling. Finally, we discuss possible experiments which may detect these predicted self-trapped states. PACS numbers: 63.20.Kr, 74.80.Dm, 73.20.Dx, 79.60.Jv Modern technology allows materials and structures with narrow bandwiths to be created. One example of such a structure is the semiconductor superlattice which can be manufactured in such a way that it can consist of different numbers of layers of differing thicknesses. In SSL consisting of say, for example, a sequence of layers of GaAs and GaxAl1−xAs, an electron miniband of width t may be created, where t is the overlapping integral for an electron localized in neighboring quantum wells. The number of levels in this miniband depend on the number of layers the SSL consists of. For example, if the superlattice consists of two quantum wells, there are only two levels associated with the symmetrical and antisymmetric wave functions. For each energy level, the probability to find the electron in either well is equally distributed. The same is true when there are many levels in the miniband. However, the situation changes dramatically if electron-phonon interactions are considered. The effect of this interaction may give rise to coupled electrons and phonons where the dimensionless electron-phonon coupling constant of this system is inversely proportional to t. Since the miniband width, in SSL, is between 1 100 meV the electron-phonon coupling is strongly