Time-resolved photoluminescence and four-wave mixing techniques have been combined for studies of carrier relaxation dynamics in a highly photoexcited GaN epilayer. For a moderate excitation density below 1 mJ/cm, carrier recombination was due to free carrier capture by deep traps. The characteristic time of carrier capture, τe = 550 ps, was measured under deep trap saturation regime. The ambip...

We use the Hanle effect to study spin relaxation in ZnxCd1−xSe epilayers grown on latticematched InP substrates. We study three samples with a fixed composition (x = 0.4) and with varying levels of n-doping, as well as an undoped sample with x = 0.5. Our measurements show that the spin relaxation time changes non-monotonically as a function of carrier density, with a maximum transverse spin lif...

Reducing hot-carrier relaxation rates is of great significance in overcoming energy loss that fundamentally limits the efficiency of solar energy utilization. Semiconductor quantum dots are expected to have much slower carrier cooling because the spacing between their discrete electronic levels is much larger than phonon energy. However, the slower carrier cooling is difficult to observe due to...

In this theoretical work, we report on voltage-controllable hybridization of electromagnetic modes arising from strong interaction between graphene surface plasmons and molecular vibrations. The interaction strength depends strongly on the volume density of molecular dipoles, the molecular relaxation time, and the molecular layer thickness. Graphene offers much tighter plasmonic field confineme...

Quantum dot (QD)-metal oxide composite forms a "heart" of the QD-sensitized solar cells. It maintains light absorption and electron-hole separation in the system and has been therefore extensively studied. The interest is largely driven by a vision of harvesting the hot carrier energy before it is lost via relaxation. Despite of importance of the process, very little is known about the carrier ...

We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO_{3}/SrTiO_{3} superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface approximately 3x10;{14} cm;{-2}. This is probably due to the leakage of d electrons at in...

A series of laser pump, x-ray probe experiments show that above band gap photoexcitation can generate a large out-of-plane strain in multiferroic BiFeO3 thin films. The strain decays in a time scale that is the same as the photo-induced carriers measured in an optical transient absorption spectroscopy experiment. We attribute the strain to the piezoelectric effect due to screening of the depola...

We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy below the band gap. We find that the spin relaxation time, measured with picosecond time resol...

Kinetics of the optical and Raman response in YBa2Cu3O6.4 were studied during room-temperature annealing following heat treatment. The superconducting Tc , dc resistivity, and low-energy optical conductivity recover slowly, implying a long relaxation time for the carrier density. Short relaxation times are observed for the B1g Raman scattering—magnetic, continuum, and phonon—and the charge tran...