A spectroscopic method is applied to measure the inelastic quasiparticle relaxation rate in a disordered Fermi liquid. The quasiparticle relaxation rate gamma is deduced from the magnitude of fluctuations in the local density of states, which are probed using resonant tunneling through a localized impurity state. We study its dependence on the excitation energy E measured from the Fermi level. In a disordered metal (heavily doped GaAs) we find that gamma~E3/2 within the experimentally accessible energy interval, in agreement with the Altshuler-Aronov theory for electron-electron interactions in diffusive conductors.

Measurements of resonant tunneling through a localized impurity state are used to probe fluctuations in the local density of states of heavily doped GaAs. The measured differential conductance is analyzed in terms of correlation functions with respect to voltage. A qualitative picture based on the scaling theory of Thouless is developed to relate the observed fluctuations to the statistics of single-particle wave functions. In a quantitative theory correlation functions are calculated. By comparing the experimental and theoretical correlation functions, the effective dimensionality of the emitter is analyzed and the dependence of the inelastic lifetime on energy is extracted.

We present spin-resolved measurements of the local density of states in Si doped GaAs. Both spin components exhibit strong mesoscopic fluctuations. In the magnetic quantum limit, the main features of the spin-up and spin-down components of the local density of states are found to be identical apart from Zeeman splitting. Based on this observation, we introduce a mesoscopic method to measure the g-factor in a material where macroscopic methods are severely restricted by disorder. Differences between the spin-up and spin-down components are discussed in terms of spin relaxation due to spin-orbit coupling.Spin-polarized electronic transport is currently attracting a lot of interest from both a fundamental and an applied point of view [1]. Spin-polarized transport is essential for the operation of spin transistors or spin valves, and recently the spin injection from a ferromagnet into a semiconductor could be observed [2]. Spin effects have also been proposed to be utilized for quantum computation. In this respect it is important to study spin relaxation and coherence in semiconductors [3].Particularly interesting spin phenomena were observed in mesoscopic semiconductor structures. Prominent examples are the Kondo effect in quantum dots [4,5] and spin-polarized tunneling through impurity levels. Resonant tunneling through impurities is also an established technique to image the local density of states (LDOS) of doped GaAs [7-10]. The LDOS exhibits mesoscopic fluctuations which can be understood in terms of interference of elastically scattered electron waves [7,8]. However, a spin-resolved measurement was impossible to date.In this paper, we investigate the spin dependence of the LDOS via resonant tunneling through a spin-split impurity level. The strongest fluctuations of the spinup and spin-down components of the LDOS are found to be identical apart from Zeeman splitting. This observation allows us to mesoscopically determine the g-factor in a material where macroscopic methods -such as photoluminescence or magnetotransport -are restricted by disorder. Differences between the spin-up and spin-down components are discussed in terms of spin relaxation due to spin-orbit coupling.Our experiment is based on a strongly asymmetric double-barrier heterostructure, which was grown on n +type GaAs substrate. It consists of a 10 nm wide GaAs quantum well and two Al 0.3 Ga 0.7 As barriers of 5 and 8 nm width. The nominally undoped active region is sandwiched between 300 nm thick GaAs contact layers doped with Si. The donor concentration has been experimentally determined to 3.3 × 10 17 cm −3 [8]. From this material we fabricated a 2 µm diameter mesa with Ohmic contacts, which contains a small number of impurities in the quantum well.We use the energetically-lowest impurity state S as spectrometer for the LDOS ν in the emitter contact adjacent to the thick barrier, see Fig. 1. In a magnetic field B, the spectrometer exhibits a spin splitting ∆E S = g S µ B B, with g S the g-factor of the impurity and µ B the Bohr magneton. The s...

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Ahstmct: Colloidal crystals of completely deionized suspensions of latex speres are subjected to oscillatory and steady shear, as well as to homogeneous and inhomogeneous electric fields. Various resonant phenomena observed in such experiments are reported. Under very slow dc-flow (v, < 7 pm s-I) the crystalline solid moves with a plug-like velocity profile, and it is excited to resonances of vp3 = 7 Hz by alternating stick-slip at the walls of stick-slip frequency v,, = 3.5 Hz. At slightly faster Flow (v,[7][8][9][10][11][12] there is depinning at all walls and the crystal moves without vibrationaI excitation, whereas increasing the flow further, results in, first, grinding of the soIid into fine crystallites, and then, shear melting and a parabolic velocity profile [I, 61.