Cubic anisotropy of hole Zeeman splitting in semiconductor nanocrystals

We study theoretically cubic anisotropy of Zeeman splitting of a hole localized in semiconductor nanocrystal. This anisotropy originates from three contributions: crystallographic cubically-symmetric spin and kinetic energy terms in the bulk Luttinger Hamiltonian and the spatial wave function distribution in a cube-shaped nanocrystal. From symmetry considerations, an effective Zeeman Hamiltonian for the hole lowest even state is introduced, containing a spherically symmetric and a cubically symmetric term. The values of these terms are calculated numerically for spherical and cube-shaped nanocrystals as functions of the Luttinger Hamiltonian parameters. We demonstrate that the cubic shape of the nanocrystal and the cubic anisotropy of hole kinetic energy (so called valence band warping) significantly affect effective $g$ factors of hole states. In both cases, the effect comes from the cubic symmetry of the hole wave functions in zero magnetic field. Estimations for the effective $g$ factor values in several semiconductors with zinc-blende crystal lattices are made. Possible experimental manifestations and potential methods of measurement of the cubic anisotropy of the hole Zeeman splitting are suggested.Comment: 17 pages, 7 figure

Theory of acceptor-ground-state description and hot photoluminescence in cubic semiconductors

An approach to the theory of the acceptor ground state in cubic semiconductors is presented. The model has been developed within the framework of the four-band effective Luttinger Hamiltonian and is applicable for both Coulomb and non-Coulomb accepters. The system of integral equations for the ground-state wave functions has been derived and its solution has been numerically computed. We present the general form of the acceptor-ground-state wave function. The wave functions for a set of acceptor dopants in GaAs are calculated with an accuracy of 2%. The obtained wave functions have been used for qualitative and quantitative analysis of the hot photoluminescence (HPL) spectra and linear polarization in GaAs crystals. Analytical expressions for the line shape and anisotropy of the linear polarization degree have been derived. The dependencies of the HPL characteristics on the excitation energy as well as on the acceptor binding energy have been analyzed. The HPL theory presented allows us to describe the wide spectrum of available experimental data

I. Studies Towards Citreamicin θ A Synthesis; II. Total Synthesis of Xanthocercin A and Methoxy-butesuperin B

Two independent projects oriented to synthesize naturally occurring compounds: a model of citreamicin θ A, and xanthocercin A with methoxy-butesuperin B. Citreamicin θ A was isolated from marine-derived bacteria Streptomyces caelestis and has been reported to possess antibacterial activity against multi-drug resistant Staph.aureus(MRSA). The key reactions in the multi-step synthesis of the citreamicin model compound involved a Sonogashira coupling and Diels-Aldercycloaddition. Xanthocercin A and methoxy-butesuperin B were isolated in a mixture with other chemical compounds from leadplant, Amorpha canescens. Due to the lack of material from natural sources, the structure and pharmaceutical properties of the compound can be confirmed only with the presence of an appropriate amount of the pure material. As part of ongoing efforts to fully verify the structure of the isolated natural products, we prepared a synthetic sample of both xanthocercin A and methoxy-butesuperin