Takeshi Suzuki

We investigated the formation dynamics of excitons and electron-hole (e-h) droplets (EHDs) in Si by using broadband terahertz time-domain spectroscopy. The formation of indirect excitons in Si was studied by observing their 1S-2P transition. Changes in surface plasmon resonance of the EHDs showed a gradual condensation from homogeneous e-h plasma at e-h densities above the exciton-Mott transition. Excitonic correlations were shown to exist prior to EHD condensation even above the Mott density.

We investigate the exciton Mott transition in Si by using optical pump and terahertz probe spectroscopy. The density-dependent exciton ionization ratio α is quantitatively evaluated from the analysis of dielectric function and conductivity spectra. The Mott density is clearly determined by the rapid increase in α as a function of electron-hole (e-h) pair density, which agrees well with the value expected from the random phase approximation theory. However, exciton is sustained in the high-densit

Photoinduced phase transitions have been intensively studied owing to their promising potential for next-generation devices. Here, the authors develop a novel analysis method: the so-called frequency-domain ARPES (FDARPES). They extend a well established measurement method of time-domain ARPES to detect how electrons are interacting with phonons during the photoinduced insulator-to-metal transition for Ta${}_{2}$NiSe${}_{5}$. They successfully unravel the underlying nature of the photoinduced ph

For the first time we have successfully measured the important cross section of the p(n, gamma)d reaction at astrophysically relevant energies between 10 and 80 keV, where the difference in the cross section between old and new calculations is quite large. In the measurement we used a prompt gamma-ray detection method, combined with a pulsed neutron beam, which is crucial for determining the cross section accurately by discriminating small true signals from huge background signals; we also used

Coherent control of a strongly inhomogeneously broadened system, namely, InAs self-assembled quantum dots, is demonstrated. To circumvent the deleterious effects of the inhomogeneous broadening, which usually masks the results of coherent manipulation, we use prepulse two-dimensional coherent spectroscopy to provide a size-selective readout of the ground, exciton, and biexciton states. The dependence on the timing of the prepulse is due to the dynamics of the coherently generated populations. To

We investigated the photoexcited carrier dynamics in Si by using optical pump and terahertz probe spectroscopy in an energy range between 2 and 25 meV. The formation dynamics of excitons from unbound $e$-$h$ pairs was studied through the emergence of the 1$s$-2$p$ transition of excitons at 12 meV (3 THz). We revealed the thermalization mechanism of the photoinjected hot carriers (electrons and holes) in the low-temperature lattice system by taking account of the interband and intraband scatterin

Inhomogeneous broadening in ensembles of semiconductor quantum dots (QDs) has hindered coherent operations due to the detuning effects, caused by the large fluctuation in the QD transition energy due to size dispersion. This difficulty is especially evident when using femtosecond laser pulses for excitation. Here, the authors successfully measure detuning-dependent coherent evolution for a QD ensemble by employing prepulse two-dimensional coherent spectroscopy. The dephasing mechanism is found t