Quantum simulations of toroidal electric ring currents and magnetic fields in linear molecules induced by circularly polarized laser pulses

Circularly polarized laser pulses may excite state selective unidirectional toroidal electric ring currents around the axis of oriented linear molecules. These in turn induce state selective magnetic fields. Quantum simulations for AlCl show that these effects are about one or even more than three orders of magnitudes larger than those which may be prepared in oriented planar molecules such as Mg-porphyrin, by means of either circularly polarized laser pulses, or by traditional magnetic fields, respectively.     

Theoretical study of14N pure quadrupole resonance in amino acids

The theoretical hybridization model of Vega is adapted to the tetrahedral environment around the nitrogen nucleus in eleven amino acids to estimate the orbital occupation numbers using the experimental values of the quadrupole coupling constant and asymmetry parameter of¹⁴N quadrupole resonance and the results are discussed.     

Identification of three-dimensional electric conductivity changes from time-lapse electromagnetic observations

We present a novel solution algorithm for 3D parameter identification based on low frequency electromagnetic data. With focus on large-scale applications such as monitoring of subsea oil production, CO₂ sequestration, and geothermal systems, the proposed solution algorithm is designed to meet challenges related to low parameter sensitivity, nonuniqueness of the inverse solutions, nonlinearity in the mapping from the data to the parameter space, and costly numerical simulations. Motivated by earlier investigations on the relation between sensitivity, nonlinearity and scale, the proposed solution approach is based on a reduced, composite parameter representation. Though a reduced representation restricts the solution space, flexibility with respect to which parameter functions that can be represented is obtained by facilitating the estimation of the structure and smoothness of the representation itself. Moreover, the resolution of the parameter function is detached from the computational grid and determined as part of the estimation. The performance of the proposed solution algorithm is illustrated through numerical examples for identification of underground electric conductivity changes from time-lapse electromagnetic observations.     

Energy transfer between excitons and plasmons in semiconductor-metal hybrid nanostructures

We summarized our recent optical studies on semiconductor nanoparticle (NP) based hybrid nanostructures: isolated CdSe NPs on Au substrates, close-packed CdSe NP monolayers on Au substrates, and close-packed monolayers of mixed CdSe/Au NPs. Luminescence properties of semiconductor-metal hybrid nanostructures were studied by space-resolved optical imaging spectroscopy and time-resolved luminescence spectroscopy. The luminescence spectra and dynamics of isolated and assembled NPs depend on the local environments. We discuss exciton-plasmon interactions in semiconductor-metal hybrid nanostructures.     

Electric dipole moments of acrylonitrile and of propionitrile measured in supersonic expansion

New determinations of the ground-state electric dipole moments of acrylonitrile and propionitrile have been made from Stark effect measurements at conditions of supersonic expansion. The measurements were made on selected Stark lobes of fully resolved hyperfine components of several lowest-J rotational transitions. The results are μ_a = 3.821(3) D, μ_b = 0.687(8) D, μ_tot = 3.882(3) D for acrylonitrile, and μ_a = 3.816(3) D, μ_b = 1.235(1) D, μ_tot = 4.011(3) D for propionitrile. The new value of μ_b for acrylonitrile is appreciably different from those reported previously and it has been substantiated by both ab initio calculations and relative intensity measurements. The new dipole moment implies a considerable revision in the calculated intensities of the strongest THz-region rotational transitions of acrylonitrile, to 59% of previous values.     

Tunable optical transmission through square-core metallic nanotube arrays

We propose a square-core metallic nanotube array and investigate its optical transmission property theoretically. We find that the transmission spectra can be tuned by the width of square-core edge, the intertube spacing and the dielectric constants of the core and the embedding medium between the nanotubes. We show that there is a band gap over a wide optical wavelength, and its width, number and position are sensitive to the tunable parameters. We also discuss the situation of the rectangular-core nanotube arrays and present that modification of the size of internal holes leads to redshift of the transmission spectra. Based on the localized nature of the field distributions, we show that there are local plasmonic resonant modes that originate from multipolar plasmon polaritons and a large number of opposing surface charges build up in the gap between adjacent nanotubes.     

Simultaneous effects of hydrostatic pressure and electric field on impurity binding energy and polarizability in coupled InAs/GaAs quantum wires

This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. Calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38 kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a non-linear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum-well wires.     

Effects of external electric and magnetic fields on the linear and nonlinear intersubband optical properties of finite semi-parabolic quantum dots

In this work, influences of external electric and magnetic fields on the optical rectification coefficient, the linear and the third-order nonlinear optical absorption coefficients as well as refractive index changes of finite semi-parabolic quantum dots are investigated. In this regard, energy eigenvalues and eigenfunctions of the system are calculated numerically, and optical properties are obtained using the compact density matrix approach. The results show that external electric and magnetic fields have a great influence on these optical quantities.     

Donor impurity states in coupled quantum well wires under hydrostatic pressure and applied electric field

In this work we study the binding energy of the ground state for a hydrogenic donor impurity in laterally coupled GaAs/Ga_1−xAl_xAs quantum well wires, considering the simultaneous effects of hydrostatic pressure and applied electric field. We have used a variational method and the effective mass and parabolic band approximations. The low dimensional structure consists of two quantum well wires with rectangular transverse section coupled by a central Ga_1−xAl_xAs barrier. Our results are reported for several sizes of the structure and we have taken into account variations of the impurity position along the growth direction of the heterostructure.     

Combined effects of electric field and hydrostatic pressure on electron states in asymmetric GaAs/(Ga,Al) triple quantum dots

The combined effects of an in-growth direction applied electric field and hydrostatic pressure on the exciton binding energy and photoluminescence energy transitions are reported in this work for triple vertically coupled quantum dots. The calculations have been carried out within the effective mass approximation, and using a variational procedure. The results show that the exciton binding energy and the photoluminescence energy transitions are functions of external probes like the hydrostatic pressure and the applied electric field.