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.

Theory of Line-Shapes of the Exciton Absorption Bands

Abstract: A general theory of line-shapes of the exciton absorption bands is developed with the help of generating function. method. When the exciton-lattice coupling is weak, and the exciton effective mass .. is ~all, the absorption band is of a Lorentzian shape, provided that the temperature T is not too high. The half-value width H is given by the level broadening of the optically produced K=O ex· citon due to lattice scattering, so that it is proportional to T except at low .temperatures. If the coupling is strong, or the exciton efFective mass is large, or the temperature is very high, the absorp­ tion band is expected to be of a Gaussian shape, and H is proportional to VT. The mutual influence of adjacent absorption bands is also discussed ; it causes the asymmetry and repulsion of the compo­ nents as temperature rises. If we replace T by the density of lattice imperfections, the ·above statements are valid, without substantial modifications, as regards the dependence on the degree of imperfections. These conclusions are in qualitative agreement with experimental data. The comparison further provides us with information on the strength of the exciton-lattice coupling and the energy band structure of the exciton.

First-principles calculations of effective-mass parameters of AlN and GaN

Abstract: The electronic band structures of the wurtzite-type AlN and GaN are calculated by using a self-consistent full-potential linearized augmented plane-wave method within the local-density-functional approximation. In order to clarify the electronic properties near the Brillouin-zone (BZ) center and to give an important guideline on the material designs for short-wavelength optical devices, we link the first-principles band calculations with the effective-mass approximation. The electronic properties are analytically studied on the basis of the effective-mass Hamiltonian, where we consider the hexagonal symmetry of the wurtzite structure. The effective-mass parameters, such as electron effective mass, hole effective masses, or, equivalently, the Luttinger-like parameters, crystal-field splitting and spin-orbit splitting, are determined by reproducing the calculated band structures near the BZ center. The obtained results show that the cubic approximation is fairly successful in the analysis for the valence-band structures of the wurtzite-type nitrides. Further, the calculated parameters for GaN are consistent with the observed ones.

Quantum Hall Effect in Polar Oxide Heterostructures

Abstract: We observed Shubnikov-de Haas oscillation and the quantum Hall effect in a high-mobility two-dimensional electron gas in polar ZnO/Mg(x)Zn(1-x)O heterostructures grown by laser molecular beam epitaxy. The electron density could be controlled in a range of 0.7 x 10(12) to 3.7 x 10(12) per square centimeter by tuning the magnesium content in the barriers and the growth polarity. From the temperature dependence of the oscillation amplitude, the effective mass of the two-dimensional electrons was derived as 0.32 +/- 0.03 times the free electron mass. Demonstration of the quantum Hall effect in an oxide heterostructure presents the possibility of combining quantum Hall physics with the versatile functionality of metal oxides in complex heterostructures.

The `Friction' of Vacuum, and other Fluctuation-Induced Forces

Abstract: The static Casimir effect describes an attractive force between two conducting plates, due to quantum fluctuations of the electromagnetic (EM) field in the intervening space. Thermal fluctuations of correlated fluids (such as critical mixtures, super-fluids, liquid crystals, or electrolytes) are also modified by the boundaries, resulting in finite-size corrections at criticality, and additional forces that affect wetting and layering phenomena. Modified fluctuations of the EM field can also account for the ``van der Waals'' interaction between conducting spheres, and have analogs in the fluctuation-induced interactions between inclusions on a membrane. We employ a path integral formalism to study these phenomena for boundaries of arbitrary shape. This allows us to examine the many unexpected phenomena of the dynamic Casimir effect due to moving boundaries. With the inclusion of quantum fluctuations, the EM vacuum behaves essentially as a complex fluid, and modifies the motion of objects through it. In particular, from the mechanical response function of the EM vacuum, we extract a plethora of interesting results, the most notable being: (i) The effective mass of a plate depends on its shape, and becomes anisotropic. (ii) There is dissipation and damping of the motion, again dependent upon shape and direction of motion, due to emission of photons. (iii) There is a continuous spectrum of resonant cavity modes that can be excited by the motion of the (neutral) boundaries.