PbTe colloidal nanocrystals: synthesis, characterization, and multiple exciton generation

We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.     

Study of CP(N-1) theta-vacua by cluster simulation of SU(N) quantum spin ladders

D-theory provides an alternative lattice regularization of the 2D CP(N-1) quantum field theory in which continuous classical fields emerge from the dimensional reduction of discrete SU(N) quantum spins. Spin ladders consisting of n transversely coupled spin chains lead to a CP(N-1) model with a vacuum angle theta=npi. In D-theory no sign problem arises and an efficient cluster algorithm is used to investigate theta-vacuum effects. At theta=pi there is a first order phase transition with spontaneous breaking of charge conjugation symmetry for CP(N-1) models with N>2.     

Raman scattering and photoluminescence studies of two-dimensional electron systems in Ge/GaAs heterostructures

Resonant Raman scattering experiments on n-Ge/n-GaAs (100) heterostructures reveal transitions involving quasi-two-dimensional electron states in Ge-accumulation layers. The experiments were performed in the range of the E₁-gap of Ge. The electronic scattering transforms into E₁-luminescence as the laser energy is tuned above the resonance. Spectra obtained at higher excitation energies show luminescence bands associated with the E₁ and E₁ + Δ₁-gap of Ge. The latter results are compared with recent data for bulk heavily-doped Ge.     

Numerical calculation of diatomic transition operators: The variable-phase and -amplitude method

The variable-phase method is extended to calculate two-atom off-the-energy shell t-matrix elements. A study is presented of the off-shell wavefunctions and t-matrix elements of the HH pair, for both the lowest ¹Σ and ³Σ interaction potentials.     

Evidence against the S-meson

Measurements are reported of p?p total cross sections from 388 to 599 MeV/c in small momentum steps. Statistical errors are typically ±0.4%and the normalisation uncertainty is ±0.7%. There is no evidence for the “S-meson”.     

Magnetic nanowires fabricated by anodic aluminum oxide template—a brief review

Anodic aluminum oxide(AAO) with highly ordered nanoscale pores which are monodisperse and mutually parallel can be produced through a self-organized electrochemical process.Subsequent deposition of materials into the nanopores produces AAO embedded nanowire arrays.Whilst the templates can be further removed to obtain free individual nanowires,the embedded nanowires form an interesting nanocomposite structure.Recent research activities on the fabrication and characteriza-tion of AAO template based magnetic n...