Being motivated by the recent result on the emergence of superlattice properties of the helical nanoribbon in an electric field, we analyze its circular dichroism signal. We theoretically demonstrate that electric-field effect on the helical nanoribbon leads to appearance of new spectral lines in circular dichroism.
Here, we analytically study optical activity of chiral semiconductor gammadions whose chirality arises from the nonuniformity of their thickness. We show that such gammadions distinguish between the two circular polarizations upon the absorption of light, unlike two-dimensional semiconductor nanostructures with planar chirality. Chiral semiconductor gammadions of inverse conical shape are found to exhibit the highest dissymmetry of optical response among the nanostructures of the same size. The results of our theoretical study can be used in future applications of semiconductor gammadions in biomedicine and optoelectronics.
We present here a simple quantum-mechanical model that describes interband optical activity of cubical semiconductor nanocrystals with chiral shape irregularities. Using the developed model, we derive the analytical expression for the rotatory strengths of interband transitions and show that the circular dichroism spectra of the chiral-shape nanocrystal consists only of the electric dipole allowed transitions. Taking into account the splitting of the valence band, one can interpret experimental circular dichroism spectra using just a few fitting parameters. The results of our study may prove useful for various branches of nanophotonics, chiral chemistry, and biomedicine.
We develop a theory of time-resolved pump–probe optical spectroscopy for modelling interband absorption by an anisotropic semiconductor nanodumbbell. By considering three transition schemes where the pump and probe pulses are nearly resonant to a dipole-allowed interband transition of different elements of the nanodumbbell, and assuming that the populations of the exited states are coupled through the nonradiative relaxation processes, we analytically calculate the absorption efficiency of the probe as a function of its delay from the pump for relatively short pulses. The obtained functional dependency, being the sum of exponentials with exponents proportional to the energy relaxation rates of the excited electronic states, is useful for the analysis of experimental absorption spectra aiming at retrieving the relaxation parameters of the nanodumbbell’s electronic subsystem.
We propose a new type of optical spectroscopy of anisotropic semiconductor nanocrystals, which is based on the welldeveloped
stationary pump-probe technique, where the pump and probe fields are absorbed upon, respectively, interband
and intraband transitions of the nanocrystals’ electronic subsystem. We develop a general theory of intraband absorption
based on the density matrix formalism. This theory can be applied to study degenerate eigenstates of electrons in
semiconductor nanocrystals of different shapes and dimentions. We demonstrate that the angular dependence of
intraband absorption by nonspherical nanocrystals enables investigating their shape and orientation, as well as the
symmetry of quantum states excited by the probe field and selection rules of electronic transitions.
We develop a theory allowing one to calculate the energy spectra and wave functions of collective excitations in twoand
three-dimensional quantum-dot supercrystals. We derive analytical expressions for the energy spectra of twodimensional
supercrystals with different Bravias lattices, and use them to analyze the possibility of engineering the
supercrystals' band structure. We demonstrate that the variation of the supercrystal’s parameters (such as the symmetry
of the periodic lattice and the properties of the quantum dots or their environment) enables an unprecedented control over
its optical properties, thus paving a way towards the development of new nanophotonics materials.
We develop a low-temperature theory of the resonant Raman scattering from a semiconductor quantum dot, whose electronic subsystem is resonant with the confined longitudinal-optical (LO) phonon modes. Our theory employs a generalized model for the quantum dot's energy spectrum renormalization, which is induced by the polar electron-phonon interaction. The model takes into account the degeneration of electronic states and allows for arbitrary LO-phonon modes to be involved in the vibrational resonance. We solve the generalized master equation for the reduced density matrix, in order to derive an analytical expression for the differential cross section of the resonant Raman scattering from a single quantum dot.