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Register a new userEffect of the Surface on the Electron Quantum Size Levels and Electron g-Factor in Spherical Semiconductor Nanocrystals
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The structure of the electron quantum size levels in spherical nanocrystals is studied in the framework of an eight--band effective mass model at zero and weak magnetic fields. The effect of the nanocrystal surface is modeled through the boundary condition imposed on the envelope wave function at the surface. We show that the spin--orbit splitting of the valence band leads to the surface--induced spin--orbit splitting of the excited conduction band states and to the additional surface--induced magnetic moment for electrons in bare nanocrystals. This additional magnetic moment manifests itself in a nonzero surface contribution to the linear Zeeman splitting of all quantum size energy levels including the ground 1S electron state. The fitting of the size dependence of the ground state electron g factor in CdSe nanocrystals has allowed us to determine the appropriate surface parameter of the boundary conditions. The structure of the excited electron states is considered in the limits of weak and strong magnetic fields.
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The temperature dependence of the electron spin $g$ factor in GaAs is investigated experimentally and theoretically. Experimentally, the $g$ factor was measured using time-resolved Faraday rotation due to Larmor precession of electron spins in the temperature range between 4.5 K and 190 K. The experiment shows an almost linear increase of the $g$ value with the temperature. This result is in good agreement with other measurements based on photoluminescence quantum beats and time-resolved Kerr rotation up to room temperature. The experimental data are described theoretically taking into account a diminishing fundamental energy gap in GaAs due to lattice thermal dilatation and nonparabolicity of the conduction band calculated using a five-level kp model. At higher temperatures electrons populate higher Landau levels and the average $g$ factor is obtained from a summation over many levels. A very good description of the experimental data is obtained indicating that the observed increase of the spin $g$ factor with the temperature is predominantly due to bands nonparabolicity.
The Zeeman splitting and the underlying value of the g-factor for conduction band electrons in GaAs/Al_xGa_{1-x}As quantum wells have been measured by spin-beat spectroscopy based on a time-resolved Kerr rotation technique. The experimental data are in good agreement with theoretical predictions. The model accurately accounts for the large electron energies above the GaAs conduction band bottom, resulting from the strong quantum confinement. In the tracked range of optical transition energies E from 1.52 to 2.0eV, the electron g-factor along the growth axis follows closely the universal dependence g_||(E)= -0.445 + 3.38(E-1.519)-2.21(E-1.519)^2 (with E measured in eV); and this universality also embraces Al_xGa_{1-x}As alloys. The in-plane g-factor component deviates notably from the universal curve, with the degree of deviation controlled by the structural anisotropy.
Contrary to the common belief that electron-electron interaction (EEI) should be negligible in s-orbital-based conductors, we demonstrated that the EEI effect could play a significant role on electronic transport leading to the misinterpretation of the Hall data. We show that the EEI effect is primarily responsible for an increase in the Hall coefficient in the La-doped SrSnO3 films below 50 K accompanied by an increase in the sheet resistance. The quantitative analysis of the magnetoresistance (MR) data yielded a large phase coherence length of electrons exceeding 450 nm at 1.8 K and revealed the electron-electron interaction being accountable for breaking of electron phase coherency in La-doped SrSnO3 films. These results while providing critical insights into the fundamental transport behavior in doped stannates also indicate the potential applications of stannates in quantum coherent electronic devices owing to their large phase coherence length.
Using the tight-binding model and the generalized Greens function formalism, the effect of quantum interference on the electron transport through the benzene molecule in a semiconductor/benzene/semiconductor junction is numerically investigated. We show how the quantum interference sources, different contact positions and local gate, can control the transmission characteristics of the electrode/molecule/electrode junction. We also study the occurrence of anti-resonant states in the transmission probability function using a simple graphical scheme (introduced in Ref.[Phys. Chem. Chem. Phys, 2011, 13, 1431]) for different geometries of the contacts between the benzene molecule and semiconductor(silicon and titanium dioxide) electrodes.
The electron-electron interactions effects on the shape of the Fermi surface of doped graphene are investigated. The actual discrete nature of the lattice is fully taken into account. A $pi$-band tight-binding model, with nearest-neighbor hopping integrals, is considered. We calculate the self-energy corrections at zero temperature. Long and short range Coulomb interactions are included. The exchange self-energy corrections for graphene preserve the trigonal warping of the Fermi surface topology, although rounding the triangular shape. The band velocity is renormalized to higher value. Corrections induced by a local Coulomb interaction, calculated by second order perturbation theory, do deform anisotropically the Fermi surface shape. Results are compared to experimental observations and to other theoretical results.
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