Y.M. Lu

The effect of Sc on the superconductivity of the BaYCu oxides

Abstract The oxide compounds of Ba 0.6 Y 0.4−x Sc x Cu (x=0.05−0.35) have been prepared. It was found that the superconducting transition temperatures of the samples vary with the contents of Sc and when Sc>0.325, the samples become nonsuperconducting.

Multiphonon Raman scattering in ZnSe/Zn0.80Cd0.20Se superlattices

Abstract A study of the multiphonon (MP) Raman scattering in ZnSe Zn 0.80 Cd 0.20 Se superlattices has been performed for the first time. Two kinds of longitudinal optical phonon modes were observed under the excitation of the 457.9 nm (2.71 eV) and 488.0 nm (2.54 eV) lines of an Ar+ ion laser at room temperature. A systematic discussion to distinguish the MP Raman scattering from hot luminescence is presented.

The Hall coefficient of YBa2Cu3O7−x thin films with (100) orientation

The Hall coefficientRH and the resistivity ρ of an (100) orientated YBa2Cu3O7-x thin film was measured. A very smallRH was obtained. The resulting carrier density is very different from the widely accepted value of the order of 1021 cm−3 for the bulk sample. The result is explained with the influence of grain boundaries and the anisotropy of the thin films.

Bipolaron interpretation of resonance Raman scattering spectra for cis-polyacetylene

Abstract A bipolaron microscopic model is proposed in this paper to theoretically interpret the resonance Raman scattering spectra in cis -polyacetylene on the basis of lattice relaxation theory. The coupling constants of electronic motion to different phonon modes are determined from the observed infrared and Raman frequencies. The theoretical results thus obtained are compared and discussed in connection with the experimental data. The method used here can applied to other similar systems.

Photoluminescence of ZnSe/Zn1 − xCdxSe strained superlattices under hydrostatic pressure

Abstract A study of the photoluminescence (PL) of ZnSe/Zn 1 − x Cd x Se strained superlattices under hydrostatic pressure (0–2.5 GPa) at room temperature has been performed for the first time. The small sublinear dependence of PL energy with pressure for the heavy-hole exciton of the well layers was observed. The pressure coefficients of the PL peak were obtained by least-squares fits to the experimental data. The linear pressure coefficient obtained by calculation is in good agreement with the experimental one.

Dispersive optical bistability in ZnCdSe-ZnSe/GaAs strained-layer superlattices on reflection at room temperature

The excitonic optical bistability with nanosecond switching time in ZnCdSe-ZnSe/GaAs strained-layer superlattices has been studied on reflection at room temperature. On the basis of the shape of the measured hysteresis loops, photoluminescence and absorption spectra, the origin of the optical bistability is attributed to the effect of excitonic saturating absorption.

The superconductivity, structure and microstructure of BaYScCu oxides

Abstract We added small amount of Sc (0.05–0.35at.%) to BaYCu oxide and found that the superconductivity deteriorated drastically when the Sc content reached 0.325at.%. X-ray and electron diffraction showed that the orthorhombic perovskite structure changed to multi-phase structure with unidentified phases. The microstructures observed by TEM are of needle like morphology. Their phases are not yet identified.

EXCITONIC PROPERTIES OF ZNSE-ZNCDSE MULTIPLE-QUANTUM WELLS UNDER HIGH-EXCITATION DENSITY

ZnSe-Zn0.78Cd0.22Se MQWs are grown on GaAs(100) substrate by MOCVD. The photoluminescence (PL) under pulsed N2 laser excitation is investigated in detail. The bands observed in PL spectra at 77K are attributed to the n = 1,2 heavy-hole exciton transitions, respectively. In high-density excitation the excitonic recombination is mainly on the exciton interaction, involves the exciton-electron (Ex-x) and exciton-exciton (Ex-Ex) interactions. The stimulated emission due to Ex-Ex scattering is observed at 77K in ZnSe-ZnCdSe MQWs.

MEASUREMENT OF NONLINEAR REFRACTIVE-INDEX AND NONLINEAR ABSORPTION-COEFFICIENT USING TRANSMISSION SPECTRUM

We present a simple, but highly sensitive, method for obtaining both the sign and magnitude of the nonlinear refractive index and the nonlinear absorption coefficient as a function of wavelength. It is shown theoretically that these parameters can be easily obtained from the linear and nonlinear transmission spectra of the medium as well as the laser intensity distribution on the frequency. This technique is demonstrated for ZnSe-ZnS multiple quantum wells on transparent CaF2 substrate at 77 K.

Excitonic Optical Nonlinearity and Optical Bistability in ZnSe–CdZnSe MQWs at Room Temperature

Excitonic optical bistability with picosecond switching time in ZnSe-CdZnSe multiple quantum wells (MQWs) optical bistable device is investigated at room temperature for the first time. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device are about 210 kW/cm2 and 2 : 1, respectively. On the basis of the excitonic nonlinear theories, excitonic absorption and excitonic emission under different excitation intensities in the ZnSe-CdZnSe MQWs obtained here, we attribute the major nonlinear mechanism for the optical bistability in ZnSe-CdZnSe MQWs optical bistable device to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.