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Electroluminescence (EL) from an Au/native silicon oxide layer structure and an structure has been observed and their EL characteristics have been studied comparatively with those from an Au/NSOL/p-Si structure. The Au/NSOL/p-Si structure emits red light only when a forward bias larger than 3 V is applied, while no light emission can be observed under reverse biases. However, the structure or the structure emits red light when the applied reverse bias is greater than a critical value around 3 V, while no light emission can be observed under forward biases. It is suggested that for EL from the and structures under reverse biases, electrons and holes which are generated in the NSOLs by impact ionization in breakdown states radiatively recombine via the luminescence centres in the NSOL to emit light.

Rare earth titanate pyrochlores are known to exhibit magnetic frustration. Large, high quality single crystals of a series of oxide pyrochlores, , have been grown by the floating zone technique, using an infrared image furnace. The crystals are roughly 5 - 6 mm in diameter and 40 - 60 mm in length and have been grown for R = Pr, Nd, Sm, Tb, Dy, Ho, Er and Y. The crystals have been characterized and tested for their quality.

This article reviews recent developments in statistical field theory far from equilibrium. It focuses on the Kardar-Parisi-Zhang equation of stochastic surface growth and its mathematical relatives, namely the stochastic Burgers equation in fluid mechanics and directed polymers in a medium with quenched disorder. At strong stochastic driving - or at strong disorder, respectively - these systems develop non-perturbative scale invariance. Presumably exact values of the scaling exponents follow from a self-consistent asymptotic theory. This theory is based on the concept of an operator product expansion formed by the local scaling fields. The key difference from standard Lagrangian field theory is the appearance of a dangerous irrelevant coupling constant generating dynamical anomalies in the continuum limit.

In this paper we consider the modulation of a SQUID ring (a Josephson weak link enclosed by a thick superconducting ring) by an external electromagnetic (em) field for the case where the ring remains adiabatically in its ground state. We demonstrate that very good agreement can be found between experimental modulation data and the results predicted theoretically by solving the time-dependent Schrödinger equation for the ring-em-field system. We also show that the non-linear dynamical coupling between the ring and an external resonant circuit can influence the exact form of the modulation. Again we find consistent agreement between experiment and theory.

A sample of lightly doped p-type porous silicon has been investigated by small-angle x-ray scattering (SAXS) at two different wavelengths (0.154 and 0.071 nm) of the probing radiation. The scattering profiles are found to have distinctly different functionality, independently indicating the importance of accounting for multiple-scattering effects. The extracted single-scattering profile can be explained in terms of mixed cylindrical and spherical pores, without recourse to fractal structures.

High-resolution neutron powder diffractometry has been used to characterize the structural phase transitions which occur in at 550 and . The change in lattice parameters of the trigonal unit cell as a function of temperature, observed in the range from ambient to , shows that the transition is associated with an abrupt contraction of the unit cell volume. The crystal structure stable in the temperature interval between 550 and is isomorphous with the stillwellite structure of in its polar variant stable up to . The phase transition at to a non-polar variant of the structure mimics the transition in . The structural parameters of these two phases have been refined from data taken at 650, 770 and . The structure of the phase stable at ambient temperature gives rise to extra reflections not given by the stillwellite structure. These can be indexed on a triple cell with and the structure has been determined and refined from a combination of neutron powder data and an ambient temperature single crystal x-ray diffraction study.

Friction is studied in a model consisting of a relatively short chain of particles (each one of which may be taken to represent a layer of atoms which is treated as rigid for simplicity) with anharmonic interparticle interactions, dragged at slow speeds over a potential which interacts with the particle on the end of the chain, with parameters chosen so that stick-slip motion takes place. A transition from dissipative to dissipationless sliding is found as a function of decreasing chain length, similar to that found for non-stick-slip motion. This could be a simplified model for a small lubricant particle anchored to a surface at one end, being dragged over a second surface at very slow speeds (about 1 cm ).

The longitudinal polarization function of a quasi-one-dimensional electron gas (Q1DEG) confined in a semiconductor quantum well wire (QWW) is given in the random-phase approximation (RPA) for the cases where T = 0 K and , taking into account the lack of spatial invariance in the plane of the cross-section of the QWW. It is given as a sum of terms in the form of a spatial function, composed from the wavefunctions, and their complex conjugates, of two single-electron states and the polarizability for each allowed transition. The polarizability for a given transition is studied in terms of its frequency, momentum and temperature dependences, relating its behaviour with the electronic topological transition occurring in the Fermi domain. The results are analysed by representing the electron gas involved in the transition as composed from two quasi-particle subgases with different effective masses within the conduction band as an excitonic gas.

Doped antiferromagnets, described by a model and a suitable expansion, exhibit a metallic phase-modulated antiferromagnetic ground state close to half-filling. Here we demonstrate that the energy of the latter state is an even periodic function of the external magnetic flux threading the square lattice in an Aharonov-Bohm geometry. The period is equal to the flux quantum entering the Peierls phase factor of the hopping matrix elements. Thus flux quantization and a concomitant finite value of superfluid weight occur along with metallic antiferromagnetism. We argue that in the context of the present effective model, whereby carriers are treated as hard-core bosons, the charge q in the associated flux quantum might be set equal to 2e. Finally, the superconducting transition temperature is related to linearly, in accordance to the generic Kosterlitz-Thouless type of transition in a two-dimensional system, signalling the coherence of the phase fluctuations of the condensate. The calculated dependence of on hole concentration is qualitatively similar to that observed in the high-temperature superconducting cuprates.

A centre in GaP having a -like behaviour has been studied both experimentally and theoretically. It was identified originally by thermally detected (TD) EPR experiments carried out at liquid helium temperatures and correlated with the optical absorption 1.03 eV zero phonon line from the isolated substitutional ion. Subsequent TD-EPR experiments on different types of samples and sub-band-gap illumination effects show that, although the centre is -like, it can not be the isolated ion. A theoretical model is proposed in which this -like ion is described by a strain-stabilized Jahn-Teller (JT) model associated with wells that have orthorhombic symmetry in the potential energy surface. On fitting the isofrequency curves to all the relevant TD-EPR data, values for the second-order JT reduction factors are obtained which indicate that this -like centre is strongly coupled to its surroundings. The electronic structure of this centre has still to be established.

We analyse the non-universal conductance fluctuations for a dirty quantum wire in a transport regime where both mesoscopic and ballistic transport characteristics play a role. This `mixed' transport regime is reached when impurities are distributed near the walls of a quantum wire, leaving the centre region ballistic. Using a diagrammatic technique, we find that the existence of a ballistic region destroys the conventional universal conductance fluctuations. The crossover behaviour of the fluctuation amplitude from the usual quasi-1D situation to that of the mixed regime is clearly revealed, and the role of various length scales identified. Our analytical predictions are confirmed by a direct numerical evaluation of the Landauer-Büttiker formula.

The two-dimensional (2D) Heisenberg model with exchange anisotropy (J < 0) and S = 1/2 is studied by the quantum Monte Carlo method. Energy and spin-spin correlation functions are calculated. The staggered magnetization dependence on anisotropy exchange is determined.

A one-step real-space renormalization group (RSRG) transformation is used to study the ferromagnetic (FM) q-state Potts model on the two-dimensional (2D) octagonal quasi-periodic tiling (OQT). The critical exponents of the correlation length for different values of q and the critical temperature of the Ising model are obtained. The results are shown to be not sensitive to the choice of parameters. The comparison of the results with previous results for the OQT and the square lattice (SQL) seems to show that the universal classes of the q-state Potts models on the OQT and the SQL are the same for the range from q = 1 to q = 3, in accordance with previous research.

The relaxation dynamics of nanoscale molecules such as arises from spin-lattice coupling and interaction with nuclear spins. Using a resolvent method in terms of the energy eigenstates and the first Born approximation with respect to phonon scattering, and averaging over the hyperfine field, we obtain a controlled approximation for the non-equilibrium magnetic relaxation behaviour and, in particular, for the corresponding rate. The rate is finite at T = 0, then increases linearly with T, and shows Arrhenius behaviour at higher temperature; for zero magnetic field B there are two different activation energies. The resonances as a function of B are shown to be slightly asymmetric about B = 0. Taking account of a quartic crystal field gives rise to a temperature-dependent shift of the resonant values of B. We find that, contrary to previous results, the rate is independent of the magnetic field at low but finite temperatures; for it is linear in B. Finally we compare our findings with various experimental data.

The optical absorption of in (RTP) and (KTP) single crystals has been characterized at 5 K and 300 K temperatures. The room temperature oscillator strengths of obtained in both lattices are similar although in KTP the uncertainty is higher due to the lower concentration of Er in the samples available. The results obtained in RTP have been analysed by using the Judd-Ofelt theory. The effective Judd-Ofelt parameters obtained for in RTP are , , . The photoluminescence transition radiative rates, branching ratios and radiative lifetimes of in these crystals have been calculated for all de-excitations from the multiplet. The erbium emission has been characterized. The low temperature optical absorption and photoluminescence suggest the coexistence of two erbium centres in both lattices, which we have tentatively ascribed to the occupancy with different population densities of the two titanium lattice sites.