Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

Latest results on J/ϕ suppression

We present preliminary results on J/? production in Pb-Pb collisions at 158 GeV/nucleon, obtained in the analysis of the most recent data sample collected by NA50 experiment in year 2000. The results are compared with an updated absorption curve deduced from new high statistics protonnucleus data. The measurements reported here confirm the anomalous J/? suppression already observed by NA50 from previously collected data samples.     

Giant piezoelectric and dielectric enhancement in disordered heterogeneous systems

Effective complex piezoelectric and dielectric constants of disordered heterogeneous systems, such as statistical mixtures consisting of spheroidal particles of the same orientation but with random distribution in space, are studied. It is found for the first time that, in such systems, there exists giant piezoelectric enhancement accompanied by giant relaxation of piezoelectric coefficients and permittivity. The piezoelectric and dielectric spectra differ considerably from the Debye spectra and have a Cole-Cole character. The dependence of the effects considered on the aspect ratios of the spheroids is investigated. The physical mechanisms responsible for the anomalous behavior of the piezoelectric coefficients and permittivity are considered.     

Nonequilibrium dynamics of quantum spin glass in an AC magnetic field

The ageing effect is studied analytically in a disordered quantum system interacting with its surroundings and subjected to an external ac magnetic field. Energy dissipation is due to the interaction of the system with a set of independent harmonic oscillators, imitating a quantum thermal bath. Dynamic equations for the autocorrelation function and linear-response function are derived using the method of closed-path integrals. The effect of an external field is studied on the correlation function and response in the spin-glass and paramagnetic phases. Both functions are found to depend on the spin interaction strength.     

Investigation of the X-ray radiation produced by a diffusive discharge in the rod-plane geometry under atmospheric pressure

Spatial parameters of the X-ray radiation produced by a high-voltage nanosecond discharge evolving in air under atmospheric pressure in the rod (cathode)-plane electrode system with a 10-cm electrode spacing are studied experimentally. A ∼170-ns voltage pulse with an amplitude of ∼200 kV and 10-ns rise time is applied to the cathode. The photoelectronic method is used to study, under the same conditions, the integrated (over the gap) characteristics of the radiation, in particular, the duration of its generation. It is found that, when the size of the X-ray source is not smaller than that of the discharge region of diffusive luminescence, radiation from the cathode region of the gap is primarily observed (i.e., from the region where the electric field distribution is sharply inhomogeneous). The X-ray generation is usually observed after the bridging of the discharge gap, the X-ray pulse having a rise time of ∼3 ns, a duration of ∼10 ns, and an effective radiation energy of ∼6 keV.     

Stimulated raman scattering in fiber-optic communication lines

Stimulated Raman scattering (SRS) in a long-distance fiber-optic communication line with wavelength-division multiplexing (WDM) is studied theoretically at a high power of the signal transmitted. A new criterion for determining the SRS threshold is used to calculate the critical input power versus the number of optical channels and frequency separation between them. The theoretical model is verified experimentally. SRS interaction between two channels in a communication line with an SRS amplifier for which the optical waveguide of the line serves as a nonlinear medium is measured.     

Addition to the Solution of the Problem on the Motion of a Free Nonrelativistic Electron in a Magnetic Field

In addition to the solution of the quantum mechanical problem on the motion of a free electron in a magnetic field, given by L. D. Landau in his pioneering work, this quantum mechanical problem is solved in view of the fact that the sum of the components of the free kinetic energy of an electron along two axes is a periodic quantity varying identically within the boundaries of every Landau energy level. This periodicity is a consequence of the quantized motion of an electron in a plane normal to the direction of the external magnetic field.