Localized optical vibrational modes in GaSb/AlSb superlattices

The vibrational spectrum of short-period GaSb/AlSb superlattices in the frequency range of GaSb optical phonons is investigated in detail. Localization of transverse GaSb optical phonons in GaSb/AlSb superlattices is observed experimentally for the first time. The dispersions of TO and LO phonons in GaSb are measured. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 361–364 (10 September 1996)     

Extended nature of coupled optical interface modes in Thue-Morse dielectric superlattices

We investigate coupled optical interface modes in Thue-Morse (TM) dielectric superlattices composed of two kinds of materials with frequency-dependent dielectric functions. Four basic transfer matrices are derived in the dielectric continuum approximation. By a standard matrix operation method, the trace map of the global transfer matrix in this configuration is obtained. Under Born-von Kármán boundary conditions, the frequency spectra are calculated and their branching rules together with the quartet property are elucidated. It is further proved rigorously that nearly all eigenmodes in this framework have extended nature. The quartet of the eigenmodes is illuminated analytically. The common features and pronounced differences compared with coupled optical interface modes in periodic and Fibonacci dielectric superlattices as well as with other collective elementary excitations in TM structures are also revealed. Received 24 September 2002 / Received in final form 11 January 2003 Published online 11 April 2003 RID="a" ID="a"e-mail: gjin@nju.edu.cn     

Raman and infrared spectroscopical investigation of the optical vibrational modes in GaSb/AlSb superlattices

The vibrational spectrum of ultra-thin layer GaSb/AlSb superlattices was investigated in detail by infrared (IR) and Raman spectroscopies. The effect of confinement of the transverse and longitudinal optical phonons in both types of the layers was studied. The dispersions of optical phonons of the GaSb and the AlSb obtained from the analysis of the Raman and IR spectra are in a good accordance with the theoretical data and results of neutron scattering experiments. First- and second-order Raman spectroscopy indicates the presence of intermixture of atoms at the interfaces in the GaSb/AlSb superlattices. Received: 11 May 1998 / Accepted: 21 July 1998     

Polariton modes in semiconductor superlattices

Polariton electric fields and dispersion relations of some important complex-basis superlattices have been derived by means of electromagnetic theory and the Bloch's theorem. The spatial distribution of the polariton electric fields shows an interesting physical picture: the polaritons are mainly bulk modes as the wavenumber k is small and become typical interface modes with very strong peak intensities as k increases.     

Collective modes in semiconductor superlattices

Electronic collective modes in a semiconductor superlattice structure are studied within the self-consistent field approach. Plasmon and magneto-plasmon dispersion relations are obtained for the cases of strong and weak coupling between layers. The interaction of these collective modes with optical phonons is also investigated.     

Higher multipole surface plasmons,plasmon bands in periodic metallic heterostructures,and plasma modes of semiconductor superlattices

The electronic collective excitations are investigated for a number of different systems whose equilibrium electron density n₀(z) is spatially varying. The relation between higher multipole surface modes, waveguide like plasma modes of a low electron density layer embedded in a high density host, and plasmon bands of periodic metallic heterostructures and semiconductor superlattices is pointed out.     

Stochastic quasi-momentum resonance in metallic superlattices

A new type of stochastic resonance excited by a longitudinal magnetic field (including a harmonic signal and noise) is studied using numerical analysis of the system of coupled magnetic moments of a multilayer metallic structure. The resonance is characterized by the phase of rest and the phase of statistical oscillations. The possibility of controlling the resonance by varying the static field, as well as the parameters of noise and the harmonic signal, is established.     

Bulk and surface magnetostatic modes in superlattices

General dispersion equations for the magnetostatic modes in infinite and semi-infinite superlattices are derived by the transfer matrix method for the case of superlattices with an elementary unit consisting of N (N arbitrary) ferromagnetic layers. The films are assumed to be magnetized parallel to the film surfaces and parallel to an external magnetic field. Explicit forms of the dispersion equations, together with exemplary dispersion curves of surface modes and bands of bulk waves, are given in the case of N = 2.     

Interface magnetic anisotropy in metallic superlattices

We have prepared Pd/M and Cu/M (M = Fe, Co, Ni) magnetic superlattices using a dc sputtering and standard UHV e-beam evaporation. Sample quality was confirmed by the intense satellite peaks in the θ−2θ X-ray diffraction patterns. For all the systems studied, torque measurements revealed positive intrinsic uniaxial anisotropy but less than 2πM²_s. Results showed that the main source of the interface anisotropy is Néel surface anisotropy.     

In掺杂ZnO超晶格光学性质的研究

采用基于第一性原理的线性缀加平面波方法, 计算了超晶格ZnO掺In的光学性质. 计算结果表明, 掺入In元素后Fermi能级进入导带, 介电函数、吸收系数、折射率、反射率都在Fermi面附近产生新的跃迁峰. 随着掺杂层数的增多, 跃迁峰发生红移, 当掺杂两层In时跃迁峰峰值最大, 同时吸收系数的吸收边随掺杂层数的增多而逐渐减小. 与In掺杂ZnO超晶胞相比, ZnO超晶格在可见光范围内具有高透过率的特点.