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.

Size-Dependent Photoluminescence from Single Indium Phosphide Nanowires

Abstract: Photoluminescence (PL) imaging and spectroscopy have been used to investigate isolated, individual indium phosphide nanowires (InP NWs) at both room temperature and 7 K PL images and spectra show that the emission maxima, line shapes, and intensities are nearly identical along the axis of a given NW PL spectra collected on InP NWs with diameters of 10, 15, 20, and 50 nm show that emission maxima systematically shift to higher energy with decreasing wire diameter, for diameters less than 20 nm An effective mass model (EMM) has been developed using particle-in-a-cylinder wave functions for electrons and holes to explore quantitatively the diameter-dependent PL data The EMM provides excellent fits to the diameter-dependent data obtained at both room temperature and 7 K, and shows that the shifts in the emission spectra can be explained by radial quantum confinement

Deep levels in semiconductors

Abstract: All defects which are dominated by short-range forces belong to the family of ‘deep’ impurities and exhibit distinctly different properties from the familiar shallow donors and acceptors, where the decisive term is the Coulomb potential. Whereas formation of the shallow states relates to a small part of the Brillouin zone and can be described within the effective mass theory, the opposite is true of the deep states. However, it has recently been shown that the formation of deep localized states in semiconductors can be described with speed and accuracy, and in a self-consistent manner, by exploiting the localized character of the main part of the defect potential. It is possible to project the interaction between the localized potential and the rest of the crystal upon a limited number of localized functions, spanning the range of the potential, with an uncertainty which is small compared to the magnitude of the forbidden gap. This is achieved without truncating proper characterization of the ele...

Repulsive Fermi Polarons in a Resonant Mixture of Ultracold ^{6}Li Atoms.

Abstract: We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

Effect of quantum fluctuations on structural phase transitions in SrTiO 3 and BaTiO 3

Abstract: Using path-integral Monte Carlo simulations and an ab initio effective Hamiltonian, we study the effects of quantum fluctuations on structural phase transitions in the cubic perovskite compounds SrTiO 3 and BaTiO 3 . We find quantum fluctuations affect ferroelectric ~FE! transitions more strongly than antiferrodistortive ~AFD! ones, even though the effective mass of a single FE local mode is larger. For SrTiO 3 we find that the quantum fluctuations suppress the FE transition completely, and reduce the AFD transition temperature from 130 to 110 K. For BaTiO3 , quantum fluctuations do not affect the order of the transition, but do reduce the transition temperature by 35‐50 K. The implications of the calculations are discussed. Quantum fluctuations typically have a very important effect on the structural and thermodynamic properties of materials consisting of light atoms like hydrogen and helium. For example, quantum effects introduce large corrections to the calculated hydrogen density distribution in the Nb:H system. 1 For materials with heavier atoms, however, the quantum fluctuation can have only a small effect on the distribution of atomic displacements, and thus typically do not have a noticeable effect on the structural and thermodynamic properties of the material. However, exceptions may occur. As we shall see, the cubic perovskites can exhibit decisive quantum-fluctuation effects, despite the fact that the lightest constituent is oxygen. This can occur because these materials have several competing structures with very small structural and energetic differences. 2

Photoluminescence in quantum-confined SnO2 nanocrystals: Evidence of free exciton decay

Abstract: Nanocrystalline SnO2 quantum dots were synthesized at room temperature by hydrolysis reaction of SnCl2. The addition of tetrabutyl ammonium hydroxide and the use of hydrothermal treatment enabled one to obtain tin dioxide colloidal suspensions with mean particle radii ranging from 1.5 to 4.3 nm. The photoluminescent properties of the suspensions were studied. The particle size distribution was estimated by transmission electron microscopy. Assuming that the maximum intensity photon energy of the photoluminescence spectra is related to the band gap energy of the system, the size dependence of the band gap energies of the quantum-confined SnO2 particles was studied. This dependence was observed to agree very well with the weak confinement regime predicted by the effective mass model. This might be an indication that photoluminescence occurs as a result of a free exciton decay process.