Ken-ichi Hino

Laser-controlled exciton Fano resonance in semiconductor superlattices

Quantum control of excitonic Floquet states in semiconductor superlattices driven by an intense monochromatic laser is examined from a theoretical point of view. High-resolution optical absorption spectra, calculated using multichannel scattering theory with the R-matrix propagation method, clarified that the excitonic Fano resonance structure is induced by the laser field. Each of the physical quantities related to this resonance-such as the spectral intensity, an asymmetry parameter (q-parameter), a resonance width, and so on-shows a characteristic extremum as a function of laser strength (F(ac)) in the vicinity of a critical value of F(ac) where dynamic localization is realized. It has also been shown that this F(ac)-dependence is caused by an ac-Zener coupling between two photon sidebands. Further, we have shown that these quantities are also controlled by changing the laser frequency (ω), as well as F(ac), and the underlying physics is explained on the basis of anticrossing behavior of the two photon sidebands.

Parallelization of the R-matrix propagation method for the study of intense-laser-driven semiconductor superlattices

Abstract Parallelization of the R-matrix propagation method for the study of intense-laser-driven semiconductor superlattices is described. We focus on photodressed excitonic electron–hole pair states related to the optical properties of the system concerned. Here, we parallelize the loop of propagation sectors, which is regarded as a rate-determining step in the whole calculation: in each sector calculated R-matrix Greenʼs functions are playing a key role. The evaluated parallelization efficiency is found sufficiently high, compared with a conventional algorithm without such parallelization. Restriction of this efficiency arising from the inter-core communications is also discussed. Further, it is shown that by virtue of the present parallelization, we readily obtain high-resolution excitonic absorption spectra revealing conspicuous dynamic Fano resonance.

Optical Response of Polarons and Solitons in One-Dimensional Peierls–Hubbard Model

We investigate optical properties of polarons and solitons in one-dimensional (1D) Peierls–Hubbard model by using the density matrix renormalization group method combined with the adiabatic approximation for lattice distortion. Obtained numerical results demonstrate that there appear novel midgap peaks in optical response spectra of polarons and charged-solitons for large on-site Coulomb interaction U . The origins of these novel peaks are understood in terms of charge-transfer excitations within clusters for each states: a dimer in polarons and a pentamer in charged-solitons, both of which are located around the center of the relaxed lattice distortion.

Laser-induced Fano resonance in semiconductor superlattice

We study excitonic Floquet states in semiconductor superlattices driven by a monochromatic laser. Optical absorption spectra are calculated by using the R-matrix propagation method, and the obtained results show the excitonic Fano resonance structure induced by the laser field. Further, physical quantities related to this resonance, such as an asymmetry parameter and a resonance width, show clear dependence on laser strength.

Significance of decay mechanism into continuum in dynamical Wannier-Stark ladder

We examine the resonance structure of photodressed electron states of laser-driven Wannier-Stark ladder, namely, dynamic Wannier-Stark ladder, in terms of the excess density of states (DOS) closely related to a lifetime of the state of concern. It is revealed that the resonance structure in the strong laser-field region shows clear dependence on the ratio, η, of a Bloch-frequency to a laser frequency. As the laser strength increases, for η = 1, the excess DOS becomes involved with a lot of newly-growing resonance peaks. This result would be understood from the viewpoint of a Fano-like decay-mechanism caused by a multichannel continuum effect, in marked contrast to the cases of larger η’s; for η = 3, the excess DOS just is found to show a pronounced red-shift of a single dominant peak caused by a single-channel continuum effect.