Density Of States And Energy Spectra Of Hydrogenic Impurities In Quantum-well Wires

We calculate binding energies and densities of states of hydrogenic impurities in quantum-well wires with rectangular cross sections using a variational procedure within the effective-mass approximation. Calculations were performed as functions of the position of the impurity in a quantum-well wire of infinite depth and for various sizes of the wire cross section. The center of gravity of the impurity band and the density of impurity states are analyzed and compared with their quantum-well counterparts, with similarities as well as differences being discussed. Our results indicate that a proper consideration of the density of impurity states may be of relevance in the interpretation of future experimental data related to shallow impurities in quantum-well wires. © 1988 The American Physical Society.3832179218

Characterization Of Resonant Tunneling Paths In Current-voltage Characteristics Line Shapes

We analyze the current density-voltage characteristics of double-barrier tunneling diodes, with different spacer layers, within the framework of a Poisson solver together with a coherent tunneling approximation for transmission probabilities. We show that varying the spacer layer thickness, together with barrier heights, changes dramatically the current density-voltage characteristics line shape, which is revealed to be an important qualitative signature of the tunneling paths involved in the double-barrier diodes under operation.© 1995 American Institute of Physics.67267

Extended state floating up in a lattice model: Bona fide levitation fingerprints, irrespective of the correlation length

The evolution of extended states with magnetic field and disorder intensities is investigated for 2D lattice models. The floating-up picture is revealed when the shift of the extended state, relative to the density of states, is properly taken into account, either for white-noise or correlated disorder.Comment: 4 pages, 4 figures. EP2DS-14 Pragu

Indented Barrier Resonant Tunneling Rectifiers

This article concerns a novel negative-conductance device consisting of a series of N laterally indented barriers which exhibits resonant tunneling under one bias polarity and simple tunneling under the opposite one, thus acting as a rectifier. Electrons undergo resonant tunneling when the bias creates a band profile with N triangular wells which can each contain a resonant state. From 1 to N the addition of each indentation can be used to increase the current density and the rectification ratio, calculated at the current-peak bias at resonance, provided that at a given bias all the states in the triangular wells align each other with the emitter Fermi energy in order to form a resonance along the structure. © 1996 American Institute of Physics.80741744176Chang, L.L., Esaki, L., Tsu, R., (1974) Appl. Phys. Lett., 24, p. 593Sollner, T.C.L.G., Goodhue, W.D., Tannenwald, P.E., Parker, C.D., Peck, D.D., (1983) Appl. Phys. Lett., 43, p. 588Sollner, T.C.L.G., Tannenwald, P.E., Goodhue, W.D., Peck, D.D., (1984) Appl. Phys. Lett., 45, p. 1319Ricco, B., Azbel, M.Ya., (1984) Phys. Rev. B, 29, p. 1970Pötz, W., (1989) J. Appl. Phys., 66, p. 2458Frensley, W.R., (1990) Rev. Mod. Phys., 62, p. 745Chevoir, F., Vinter, B., (1993) Phys. Rev. B, 47, p. 7260Chang, L.L., Mendez, E.E., Tejedor, C., (1991) Resonant Tunneling in Semiconductors: Physics and Applications, , Plenum, New YorkSollner, T.C.L.G., Brown, E.R., Goodhue, W.C., Microwave and Milimeter-Wave Resonant Tunneling Diodes (1987) Picosecond Electronics and Optoelectronics Technical Digest, 87 (1), pp. 143-145. , Optical Society of America, Washington, D.CLiu, H.C., Coon, D.D., (1987) Appl. Phys. Lett., 50, p. 1669Schulz, P.A., Da Silva, G., (1988) Appl. Phys. Lett., 52, p. 960Papp, G., Di Ventra, M., Coluzza, C., Baldereschi, A., Margaritondo, G., (1995) Superlattices Microstruct., 17, p. 273Di Ventra, M., Papp, G., Coluzza, C., Baldereschi, A., (1994) Proceedings of the 22nd International Conference on the Physics of Semiconductors, p. 1600. , edited by D. J. Lockwood World Scientific, SingaporeVassel, M.O., Lee, J., Lockwood, H.F., (1983) J. Appl. Phys., 54, p. 5206Papp, C., Coluzza, C., Di Ventra, M., Baldereschi, A., Margaritondo, G., Gu, B.-Y., (1995) Superlattices Microstruct., 17, p. 117Adachi, S., (1985) J. Appl. Phys., 58, pp. R1Rossmanith, M., Syassen, K., Böckenhoff, E., Ploog, K., Von Klitzing, K., (1991) Phys. Rev. B, 44, p. 3168Ohno, H., Mendez, E.E., Wang, W.I., (1990) Appl. Phys. Lett., 56, p. 1793Guéret, P., Rossel, C., Marclay, E., Meier, H., (1989) J. Appl. Phys., 66, p. 278Guéret, P., Rossel, C., Schulp, W., Meier, H., (1989) J. Appl. Phys., 66, p. 431

Coulomb gap in one-dimensional disordered electronic systems

We study a one-dimensional system of spinless electrons in the presence of a long-range Coulomb interaction (LRCI) and a random chemical potential at each site. We first present a Tomonaga-Luttinger liquid (TLL) description of the system. We use the bosonization technique followed by the replica trick to average over the quenched randomness. An expression for the localization length of the system is then obtained using the renormalization group method and also a physical argument. We then find the density of states for different values of the energy; we get different expressions depending on whether the energy is larger than or smaller than the inverse of the localization length. We work in the limit of weak disorder where the localization length is very large; at that length scale, the LRCI has the effect of reducing the interaction parameter K of the TLL to a value much smaller than the noninteracting value of unity.Comment: Revtex, 6 pages, no figures; discussions have been expanded in several place

The random phase property and the Lyapunov Spectrum for disordered multi-channel systems

A random phase property establishing in the weak coupling limit a link between quasi-one-dimensional random Schrödinger operators and full random matrix theory is advocated. Briefly summarized it states that the random transfer matrices placed into a normal system of coordinates act on the isotropic frames and lead to a Markov process with a unique invariant measure which is of geometric nature. On the elliptic part of the transfer matrices, this measure is invariant under the unitaries in the hermitian symplectic group of the universality class under study. While the random phase property can up to now only be proved in special models or in a restricted sense, we provide strong numerical evidence that it holds in the Anderson model of localization. A main outcome of the random phase property is a perturbative calculation of the Lyapunov exponents which shows that the Lyapunov spectrum is equidistant and that the localization lengths for large systems in the unitary, orthogonal and symplectic ensemble differ by a factor 2 each. In an Anderson-Ando model on a tubular geometry with magnetic field and spin-orbit coupling, the normal system of coordinates is calculated and this is used to derive explicit energy dependent formulas for the Lyapunov spectrum

Coulomb gap in one-dimensional disordered electron systems

The density of states of one-dimensional disordered electron systems with long range Coulomb interaction is studied in the weak pinning limit. The density of states is found to follow a power law with an exponent determined by localization length, and this power law behavior is consistent with the existing numerical results.Comment: RevTeX4 file, 5 pages, no figures To appear in Physical Reviews

Conductivity Of Polymer Chains: A Tunneling Approach

We investigate the effect of disorder in the conductivity of polyaniline chains. We adopt a tunneling approach coupled to a simplified Hamiltonian, in which we model the ring-structured polymer as a linear chain of pseudoatoms. To adjust the Hamiltonian parameters, we rely on previously published data on the electronic structure for such chains. Our results agree with available data on the behavior of conductivity with protonation dose, and thus give support to the disordered-chain model of polyanilines. © 1991 The American Physical Society.44126073607

Simple Model For Resonant Tunneling Beyond The Effective-mass Approximation

We evaluate, within a single-band tight-binding model, the resonant transmission probability for a particle through a symmetric barrier-well-barrier potential structure. This is a simplified model of resonant tunneling through (Ga,Al)As-GaAs-(Ga,Al)As heterostructure. We examine both the cases of minimum of the band states at the center (direct-gap tunneling) and at the edge (indirect-gap tunneling) of the Brillouin zone for the barrier material. We show that only the lowest traveling-wave energy states, irrespective of their symmetry, dominate the tunneling. © 1987 The American Physical Society.35158126813

Co-authorship networks and research impact in large research facilities: benchmarking internal reports and bibliometric databases

In this paper, we address the main differences of the scientific production between internal and external researcher groups of a synchrotron radiation facility. Through the construction and analysis of their co-authorship networks, we could see the structural variations in the way these two different kinds of research groups collaborate. We also evaluated the scientific impact of each group and found surprising similarities, which led us to create two hypotheses that might contribute to the comprehension of the scientific assessment of large-scale research facilities. We found that, as the review criteria the studied synchrotron adopts to select external scientific projects is very effective; the quality of the external research is at least as good as the internal. Therefore, evaluating the internal scientific output appears to be an appropriate representation of the impact of the whole laboratory.Merit, Expertise and Measuremen