Three-dimensional topological insulator based nanospaser

Abstract

After the discovery of the spaser (surface plasmon amplification by stimulated emission of radiation), first proposed by Bergman and Stockman in 2003, it has become possible to deliver optical energy beyond the diffraction limit and generate an intense source of an optical field. The spaser is a nanoplasmonic counterpart of a laser. One of the major advantages of the spaser is its size: A spaser is a truly nanoscopic device whose size can be made smaller than the skin depth of a material to a size as small as the nonlocality radius ($\ensuremath{\sim}1$ nm). Recently, an electrically pumped graphene based nanospaser has been proposed that operates in the midinfrared region and utilizes a nanopatch of graphene as a source of plasmons and a quantum-well cascade as its gain medium. Here we propose an optically pumped nanospaser based on three-dimensional topological insulator (3D TI) materials, such as ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, that operates at an energy close to the bulk band-gap energy $\ensuremath{\sim}0.3$ eV and uses the surface as a source for plasmons and its bulk as a gain medium. Population inversion is obtained in the bulk and the radiative energy of the exciton recombination is transferred to the surface plasmons of the same material to stimulate spasing action. This is truly a nanoscale spaser as it utilizes the same material for dual purposes. We show theoretically the possibility of achieving spasing with a 3D TI. As the spaser operates in the midinfrared spectral region, it can be a useful device for a number of applications, such as nanoscopy, nanolithography, nanospectroscopy, and semiclassical information processing.