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The philosophy behind this work has been to build a predictive “bottom up” physical model of quantum cascade lasers (QCLs) for use as a design tool, to interpret experimental results and hence improve understanding of the physical processes occurring inside working devices and as a simulator for developing new material systems. The standard model uses the envelope function and effective mass approximations to solve two complete periods of the QCL under an applied bias. Other models, such as k·p and empirical pseudopotential, have been employed in p-type systems where the more complex band structure requires it. The resulting wave functions are then used to evaluate all relevant carrier–phonon, carrier–carrier and alloy scattering rates from each quantised state to all others within the same and the neighbouring period. This information is then used to construct a rate equation for the equilibrium carrier density in each subband and this set of coupled rate equations are solved self-consistently to obtain the carrier density in each eigenstate. The latter is a fundamental description of the device and can be used to calculate the current density and gain as a function of the applied bias and temperature, which in turn yields the threshold current and expected temperature dependence of the device characteristics. A recent extension which includes a further iteration of an energy balance equation also yields the average electron (or hole) temperature over the subbands. This paper will review the method and describe its application to mid-infrared and terahertz, GaAs, GaN, SiGe cascade laser designs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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Abstract: Datailed muon level-crossing resonance measurements of Mu1 and Mu11 centres in single crystals of CuCl are presented. The hyperfine and nuclear hyperfine parameters of the closest two shells of nuclei are remarkably similar for the two centres, indicating that both are located at the same tetrahedral interstitial site with four Cu nearest neighbours and six Cl next-nearest neighbours. About 30% of the total unpaired-electron spin density is located on the muon, about 60% on the four nearest neighbours and the rest on the six next-nearest neighbours, with nothing observable for any other shell.

Abstract: A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa2Cu3O x samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen contentx was found to have strong similarities with the behavior of the critical temperatureT c as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups.

Abstract: Planar channeling data ofμ +-decay positrons in various semiconductors are reported. Together with the extensive spectroscopic data supplied by transverse μSR, the location of the different states of the hydrogen pseudo-isotopeμ + e− (muonium) can be identified by means of planar simulations. In high purity silicon as well as in gallium arsenide a thermally activated site transition is observed which can be assigned to a transition between different muonium states.

Muon spin rotation (µSR) measurements of the internal magnetic fields in sintered YBa2Cu3O7-d samples are reported. Pronounced differences between field-cooled (FC) and zero-field-cooled (ZFC) µSR signals, hysteresis effects and flux trapping are observed. The µSR results are compared with the results of macroscopic experiments (susceptibility, magnetization, resistivity) and with predictions obtained from models of weakly-coupled superconducting regions.

We present a simple method to obtain reliable ground-state entropies of Ising antiferromagnets in a maximum critical field. As an example, the ground-state entropy for the square lattice is established for allS. Both the case of the first-, and of the second-neighbour interactions are considered.

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WITH present knowledge and techniques, a more meaningful application of biochemical data towards classification schemes may be made at the family level and lower1.