Currents and pseudomagnetic fields in strained graphene rings

We study the effects of strain on the electronic properties and persistent current characteristics of a graphene ring using the Dirac representation. For a slightly deformed graphene ring flake, one obtains sizable pseudomagnetic (gauge) fields that may effectively reduce or enhance locally the applied magnetic flux through the ring. Flux-induced persistent currents in a flat ring have full rotational symmetry throughout the structure; in contrast, we show that currents in the presence of a circularly symmetric deformation are strongly inhomogeneous, due to the underlying symmetries of graphene. This result illustrates the inherent competition between the `real' magnetic field and the `pseudo' field arising from strains, and suggest an alternative way to probe the strength and symmetries of pseudomagnetic fields on graphene systems

Infrared-absorption Line Shapes Of Shallow Donors In Cylindrical Quantum-well-wire Structures

A theoretical study of the intraimpurity infrared-absorption properties associated to donor-doped cylindrical GaAs-(Ga,Al)As quantum-well wires is presented. Donor binding energies and envelope wave functions are calculated within a variational scheme in the effective-mass approximation, and line strengths for intradonor transitions to excited states of 2s-, 2pz-, and 3pz-like symmetries are obtained for different photon polarizations and for donor positions varying along the radial direction of the wire. The donor-related absorption coefficients are evaluated in the case of 1s→2pz and 1s→3pz transitions for z-polarized radiation, and for different donor profiles in the quantum wire. © 1995 American Institute of Physics.7731328133

Rabi oscillations, coherent properties, and model qubits in two-level donor systems under terahertz radiation

Quantum confinement, magnetic-field effects, and laser coupling with the two low-lying states of electrons bound to donor impurities in semiconductors may be used to coherently manipulate the two-level donor system in order to establish the appropriate operational conditions of basic quantum bits (qubits) for solid-state based quantum computers. Here we present a theoretical calculation of the damped Rabi oscillations and time evolution of the 1s and 2p(+) donor states in bulk GaAs under an external magnetic field and in the presence of terahertz laser radiation, and their influence on the measured photocurrent. We also discuss the possible experimental conditions under which decoherence is weak and qubit operations are efficiently controlled.682

Dressed-band approach and Coulomb corrections to the light-induced exciton Stark shift

In the present work, we perform a comparison of theoretical approaches involving Coulomb-interaction corrections within the Hartree-Fock approximation and the renormalized dressed-band scheme in the large detuning limit. We focus on the well-studied optical Stark shift of the exciton peak in bulk and GaAs-(Ga,Al)As semiconductor quantum wells. It is argued that the Hartree-Fock scheme has severe limitations concerning its application to real experimental situations, even in the simplest laser field-perturbative regime. It is also shown, through a comparison between experiments and a three-band Kane-dressed GaAs-(Ga,Al)As quantum well calculation, that a proper treatment of band structure and confinement effects due to the quantum well is of fundamental importance in a theoretical understanding of Stark shift experimental measurements, and that the renormalized dressed-band approach is a very convenient tool to treat, in the large detuning limit, processes involving the laser-semiconductor interaction in low-dimensional heterostructures. (C) 2003 American Institute of Physics.9495742574

Effects Of External Fields On The Far-infrared 1s→2p+ Intradonor Absorption Spectra In Quantum Wells

The effects of both electric and magnetic fields (applied perpendicular to the interfaces) on the donor transition energies on a GaAs-Ga1-xAlxAs quantum well are studied by following a variational calculation within the effective-mass approximation with two-parameter variational envelope hydrogenic wave functions for the 1s- and 2p+-like donor states. A detailed analysis of the far-infrared intradonor absorption spectra, taking into account a proper consideration of the impurity-doping profile, is performed and results are compared with recent experimental data. The agreement between the reported magnetospectroscopic data and the average photon energy at the width at half-maximum of the calculated infrared-absorption spectra is quite apparent. It is unambiguously shown that the absorption spectra must be evaluated with an adequate choice of the variational envelope wave function for a correct quantitative understanding of the experimental measurements. © 1996 American Institute of Physics.80425362538Parihar, S.R., Lyon, S.A., (1993) Appl. Phys. Lett., 62, p. 2396Jarosik, N.C., McCombe, B.D., Shanabrook, B.V., Comas, J., Ralston, J., Wicks, G., (1985) Phys. Rev. Lett., 54, p. 1283Barmby, P.W., Dunn, J.L., Bates, C.A., (1994) J. Phys. Condens. Matter, 6, p. 751. , and references thereinChen, R., Cheng, J.P., Lin, D., McCombe, B.D., George, T.F., (1995) J. Phys. Condens. Matter, 7, p. 3577. , and references thereinLatgé, A., Porras-Montenegro, N., Oliveira, L.E., (1995) Phys. Rev. B, 51, p. 2259(1995) Phys. Rev. B, 51, p. 13344Latgé, A., Porras-Montenegro, N., De Dios-Leyva, M., Oliveira, L.E., (1996) Phys. Rev. B, 53, p. 10160Barbosa, L.H.M., Latgé, A., De Dios-Leyva, M., Oliveira, L.E., (1996) Solid State Commun., 98, p. 215Yoo, B.S., McCombe, B.D., Schaff, W., (1991) Phys. Rev. B, 44, p. 13152López-Gondar, J., D'Albuquerque E Castro, J., Oliveira, L.E., (1990) Phys. Rev. B, 42, p. 7069Greene, R.L., Bajaj, K.K., (1985) Phys. Rev. B, 31, p. 913(1986) Phys. Rev. B, 34, p. 951(1988) Phys. Rev. B, 37, p. 4604Chaudhuri, S., Bajaj, K.K., (1984) Solid State Commun., 52, p. 967(1984) Phys. Rev. B, 29, p. 1803Greene, R.L., Lane, P., (1986) Phys. Rev. B, 34, p. 8639(1986) Phys. Rev. B, 33, p. 587

Acceptor-related Photoluminescence Spectra Of Gaas Quantum-wire Microcrystals: A Model Calculation

The acceptor-related photoluminescence spectrum of a GaAs quantum-wire microcrystal is investigated theoretically using a model calculation within the effective-mass approximation, with the acceptor envelope wave functions and binding energies calculated by a variational procedure. Typical theoretical photoluminescence spectra show two peaks associated with transitions from the n=1 conduction-subband electron gas to acceptors at the on-center and on-edge positions in the wire, in good agreement with the recent experimental results by Hiruma et al. [Appl. Phys. Lett. 59, 431 (1991)]. © 1993 The American Physical Society.47201386413867Akamai Technologies, Inc.,IEEE Computer Society Technical Committee on Distributed Processing (TCDP),IEEE Computers Society,International Research Institute on Autonomic Network Computing,Technical Committee on Distributed Processin

DONOR-EXCITED STATES AND INFRARED-TRANSITION STRENGTHS IN CYLINDRICAL GAAS-(GA,AL)AS QUANTUM-WELL WIRES

A variational calculation within the effective-mass approximation of the ground and lowest excited states of a donor impurity in a cylindrical GaAs-(Ga,Al)As quantum-well wire is presented. The corresponding impurity binding energies are calculated for various values of the GaAs-(Ga,Al)As quantum-wire radius and donor positions within the wire. The line strengths of transitions from the donor ground state to excited states of 2s-like and 2p(z)-like symmetries are calculated as the donor position varies along the radial direction in the wire, for polarizations of the incident radiation perpendicular and parallel to the wire axis, respectively. Although the 1s-->2s donor transition is forbidden in bulk materials, this transition is allowed for incident radiation polarized along the y radial direction of the wire with a quite considerable oscillator strength-comparable to the strength of the 1s-->2p(z) transition-for impurities away from the wire axis.4915104501045