Effective mass (solid-state physics)

About: Effective mass (solid-state physics) is a research topic. Over the lifetime, 12539 publications have been published within this topic receiving 295485 citations.

A simple theory of the electron-phonon mass enhancement in transition metals

Abstract: Using information available from band structure calculations, neutron scattering experiments and a simple theory of the electron-phonon coupling. The mass enhancement factor lambda is calculated for ten transition metals: Zr, Nb, Mo, Ta, W, Re, Rh, Pd, Ir and Pt. For the superconducting elements the results are in good qualitative and in reasonable quantitative agreement with the empirical values of lambda obtained from data on the superconducting transition temperature. The magnitude of lambda in the nonsuperconducting metals is discussed.

Optical and Electronic Transport Properties of Electrodeposited Thallium(III) Oxide Films

Abstract: Thallium oxide is a degenerate n-type semiconductor which can be electrodeposited from aqueous solution at room temperature. Thin films were characterized by transmission and specular reflectance spectroscopy and by four-point resistivity and Hall measurements. Optical parameters were determined by fitting the observed specular reflectance to the Drude equation. Due to the high free carrier concentration, the material reflects strongly in the near-infrared, and the band-to-band optical transitions are shifted by up to 1.1 eV by the Moss-Burstein effect. The optical and electrical properties of the films were a function of the deposition overpotential. Films grown at 44 mV had an intrinsic bandgap of 0.66 eV, resistivity of 2.8 x 10{sup -4} ohm-cm, mobility of 27 cm{sup 2}Vs, and conduction band effective mass of 0.43m{sub o}. Films grown at 300 mV had an intrinsic band gap of 0.51 eV, resistivity of 7.8 x 10{sup -5} ohm cm, mobility of 93 cm{sup 2}V s, and conduction band effective mass of 0.29m{sub o}. Mobilities measured by contact and optical methods are similar, which shows the optical technique may be used for conditions in which contact methods might fail. 20 refs., 11 figs., 2 tabs.

An Introduction to Relativistic Quantum Chemistry

Abstract: Chemistry is governed by the shell structure of the atoms. This holds in particular concerning the periodic system of chemical elements. Non-relativistic quantum chemistry describes the motion of electrons and nuclei and their mutual interactions to a first approximation. It reproduces a large fraction of chemistry of the more important lighter elements sufficiently well. A significant amount of chemical insight can already be gained from the analysis of the atomic one-electron orbitals. However, while valence electrons have ‘non-relativistically small’ energies, they become ‘relativistically fast’ in the neighborhood of heavy nuclei. The importance of relativistic effects in the atomic valence shells increases approximately as Z2. Relativity significantly changes the chemical trends at the bottom of the periodic table. The relativistic effects of the valence electrons can be classified as direct and indirect ones. The direct ones are due to the increase of the effective mass with velocity, to the change of the electric nuclear attraction of a spinning electron, and to the magnetic spin-orbit coupling. The indirect effects on the valence electrons are due to the relativistic changes of nuclear shielding and Pauli repulsion by the inner orbitals. The changes of the radial, the angular, and the quaternionic phase behavior of the relativistic atomic valence orbitals modify the atomic bonding properties, the energetics, the structure and properties of the molecules.

Donor-impurity related binding energy and photoinization cross-section in quantum dots: electric and magnetic fields and hydrostatic pressure effects

Abstract: We have studied the behavior of the binding energy and photoionization cross-section of a donor-impurity in cylindrical-shape GaAs-Ga0.7Al0.3As quantum dots, under the effects of hydrostatic pressure and in-growth direction applied electric and magnetic fields. We have used the variational method under the effective mass and parabolic band approximations. Parallel and perpendicular polarizations of the incident radiation and several values of the quantum dot geometry have also been considered. Our results show that the photoionization cross-section growths as the hydrostatic pressure is increased. For parallel polarization of the incident radiation, the photoionization cross-section decreases when the impurity is shifted from the center of the dot. In the case of perpendicular polarization of the incident radiation, the photoionization cross-section increases when the impurity is shifted in the radial direction of the dot. For on-axis impurities the transitions between the ground state of the impurity and the ground state of the quantum dot are forbidden. In the low pressure regime (less than 13.5 kbar) the impurity binding energy growths linearly with pressure, and in the high pressure regime (higher than 13.5 kbar) the binding energy growths up to a maximum and then decreases. Additionally, we have found that the applied electric and magnetic fields may favor the increase or decrease in binding energy, depending on the impurity position.