The ultrafast relaxation and recombination dynamics of photogenerated electrons and holes in epitaxial graphene are studied using optical-pump terahertz-probe spectroscopy. The conductivity in graphene at terahertz frequencies depends on the carrier concentration as well as the carrier distribution in energy. Time-resolved studies of the conductivity can therefore be used to probe the dynamics ...

Quantum Monte Carlo calculations of the relaxation energy, pair-correlation function, and annihilating-pair momentum density are presented for a positron immersed in a homogeneous electron gas. We find smaller relaxation energies and contact pair-correlation functions in the important low-density regime than predicted by earlier studies. Our annihilating-pair momentum densities have almost zero...

The authors report a direct measurement of the optical phonon intersubband hole relaxation time in a SiGe heterostructure and a quantitative determination of hole relaxation under electrically active conditions. The results were obtained by femtosecond resolved pump-pump photocurrent experiments using a free electron laser wavelength 7.9 m . Additionally, the intensity dependence of the nonline...

Site-directed spin labeling in combination with EPR is a powerful method for providing distances on the nm scale in biological systems. The most popular strategy, double electron-electron resonance (DEER), is carried out at cryogenic temperatures (50-80 K) to increase the short spin-spin relaxation time (T2) upon which the technique relies. A challenge is to measure long-range distances (20-60 ...

Wehave studied nuclear effects on electron spins in lightly doped n-GaAs bulk and quantumwell samples using optically detected magnetic resonance, with the optical detection done via Kerr rotation. The magnetic resonance signal allowed us to measure the electron T ∗ 2 lifetimes and g-factors. We observed strong dynamic nuclear polarization, which was controllable via nuclear magnetic resonance ...

Quantum Hall effect (based on http://www.pha.jhu.edu/~qiuym/qhe/) Basics of Hall Effect In the Drude theory of the electrical conductivity of a metal, an electron is accelerated by the electric field for an average time , the relaxation or mean free time, before being scattered by impurities, lattice imperfections and phonons to a state which has average velocity zero. The average drift velocit...

Decoherence of a shallow donor electron spin in silicon caused by electron-lattice interaction is studied. We find that there are two time scales associated with the evolution of the electron spin density matrix: the fast but incomplete decay due to the interaction with non-resonant phonons followed by slow relaxation resulting from spin flips accompanied by resonant phonon emission. We estimat...

The femtosecond intraband relaxation of hot carriers in GaAs, Al03 2Ga0 68 As, and the multiple-quantum-well structure is studied using the equal-pulse optical-correlation technique. An overview of the experimental application of this technique to semiconductors is presented. A detailed theoretical analysis of the coherent-artifact contribution to the transmission-correlation peak in the geomet...

Detailed self-consistent calculations have been performed of the electron transport and capture aspects of the dynamics of electrically pumped quantum cascade intersubband semiconductor lasers. Specific attention is given to the dependence of the characteristic carrier relaxation times on carrier temperature and density at different applied biases. We have found that the capture and intersubban...