RESUMO
We theoretically introduce a topological spaser, which consists of a hexagonal array of plasmonic metal nanoshells containing an achiral gain medium in their cores. Such a spaser can generate two mutually time-reversed chiral surface plasmon modes in the K and K^{'} valleys, which carry the opposite topological charges, ±1, and are described by a two-dimensional E^{'} representation of the D_{3h} point symmetry group. Due to the mode competition, this spaser exhibits a bistability: only one of these two modes generates, which is a spontaneous symmetry breaking. Such a spaser can be used for an ultrafast all-optical memory and information processing, and biomedical detection and sensing with chirality resolution.
RESUMO
Using magneto-infrared spectroscopy, we have explored the charge dynamics of (Bi,Sb)2Te3 thin films on InP substrates. From the magneto-transmission data we extracted three distinct cyclotron resonance (CR) energies that are all apparent in the broad band Faraday rotation (FR) spectra. This comprehensive FR-CR data set has allowed us to isolate the response of the bulk states from the intrinsic surface states associated with both the top and bottom surfaces of the film. The FR data uncovered that electron- and hole-type Dirac Fermions reside on opposite surfaces of our films, which paves the way for observing many exotic quantum phenomena in topological insulators.
RESUMO
We investigate resonance energy transfer (RET) between a donor-acceptor pair above a gold surface (including bulk and thin-film systems) and explore the distance/frequency dependence of RET enhancements using the theory we developed previously. The mechanism of RET above a gold surface can be attributed to the effects of mirror dipoles, surface plasmon polaritons (SPPs), and retardation. To clarify these effects on RET, we analyze the enhancements of RET by the mirror method, the decomposition of s- and p-polarization, and the SPP dispersion of charge-symmetric and charge-antisymmetric modes. We find a characteristic distance (approximately 1/10 of the wavelength) that can be used to classify the dominant effect on RET. Moreover, the characteristic distance can be shortened by narrowing the thickness of the thin-film systems, indicating that SPPs can enhance the rate of RET at a short range. The charge-symmetric and charge-antisymmetric modes of the thin films also allow us to engineer the maximum RET enhancement. We hope that our analysis inspires further investigation into the mechanism of RET coupled with SPPs and its applications.