No abstract

We report unusual photoluminescence (PL) behaviors in highly photoexcited SrTiO(3) crystals at low temperatures. The PL spectrum and dynamics show abrupt changes below 150 K in both nondoped and electron-doped SrTiO(3) samples. We clarified that the PL dynamics in both nondoped and electron-doped SrTiO(3) is well described by the same simple model involving single-carrier trapping, radiative bimolecular recombination, and nonradiative Auger recombination. The unusual temperature dependence of PL dynamics is caused by the crossover from Auger recombination at high temperatures to single-carrier trapping at low temperatures. We discuss the temperature-dependent PL dynamics in conjunction with the high carrier mobility of SrTiO(3) at low temperatures.

We studied the splitting instability of a quadruply charged vortex both experimentally and theoretically. The density defect, which is a signature of the vortex core, is experimentally observed to deform into a linear shape. The deformed defect is theoretically confirmed to be an array of four linearly aligned singly charged vortices. The array of vortices rotates and precesses simultaneously with different angular velocities. The initial state of the system is not rotationally symmetric, which enables spontaneous splitting without external perturbations.

We studied photocarrier recombination processes in highly excited SrTiO 3 crystals using pump-probe transient absorption ͑TA͒ and photoluminescence ͑PL͒ spectroscopy at room temperature. TA signals of nondoped SrTiO 3 crystals clearly appear in the visible and infrared spectral region under intense interband photoexcitation, and TA spectra show Drude-like photon-energy dependence. Both TA and PL decay curves are well explained by the same simple rate equation including three-body Auger recombination and single-carrier trapping.

We report on the optical determination of the carrier-density profiles near surfaces in SrTiO 3 crystals by means of photoluminescence ͑PL͒ dynamics measurements. The PL dynamics under band-to-band excitation depends strongly on the excitation photon energy for different optical penetration depths. In nondoped and Ar + -irradiated SrTiO 3 crystals, we evaluate the depth profile of carriers near the surface based on the lifetime of the Auger recombination of electrons originating from oxygen vacancies with photocarriers. Our PL spectroscopy clarifies that in nondoped SrTiO 3 , the near-surface oxygen-deficient region is a few tens of nanometers in depth.

We report the observation of a remarkably strong coupling between light and a multinode-type exciton. The observed radiative decay time reaches the order of 100 fs, which is much faster than the dephasing process of nonradiative scattering. In this high-speed superradiance, the light wave and the excitonic wave in a high-quality thin film form a harmonized wave-wave coupling over a range of multiple wavelengths. This mechanism contradicts the conventional physical description of light-matter interaction based on the long-wavelength approximation.

No abstract

No abstract