Energy Level Shifts Research Articles

Effects of Quantum well Size Alteration on Excitonic Population Oscillation Slow Light Devices Properties

This paper investigates the effects of quantum well size changes on center frequency and slow down factor of an slow light device. In this way, we consider the quantum well size alteration effects on oscillator strength and binding energy of exciton. First, we investigate the variations in oscillator strength of exciton due to different quantum well size. Second, exciton binding energy level shift due to size of quantum well is investigated. According to this analysis, we have developed a new method for tuning slow light device bandwidth center frequency and slow down factor. Analysis and simulation of a basic GaAs/AlGaAs quantum wells optical slow light device based on excitonic population oscillation shows that size of quantum wells could tune both of the frequency properties and slow down factor of an optical slow light device. In our simulation with 34 quantum wells each with the width of 60?, we have received the slow down factor of more than 60,000. These achievements are useful in optical nonlinearity enhancements, all-optical signal processing applications and optical communications.

Quantum electrodynamics near anisotropic polarizable materials: Casimir-Polder shifts near multilayers of graphene

In a recent paper we have formulated a theory of non-relativistic quantum electrodynamics in the presence of an inhomogeneous Huttner-Barnett dielectric. Here we generalize the formalism to anisotropic materials and show how it may be modified to include conducting surfaces. We start with the derivation of the photon propagator for a slab of material and use it to work out the energy-level shift near a medium whose conductivity in the direction parallel to the surface far exceeds that in the direction perpendicular to the surface. We investigate the influence of the anisotropy of the material's electromagnetic response on the Casimir-Polder shifts, both analytically and numerically, and show that it may have a significant impact on the atom-surface interaction, especially in the non-retarded regime, i.e. for small atom-surface separations. Our results for the energy shift may be used to estimate the Casimir-Polder force acting on quantum objects close to multilayers of graphene or graphite. They are particularly important for the case of trapped cold molecules whose dispersive interactions with surfaces often fall within the non-retarded regime where the anisotropy of the material strongly influences the Casimir-Polder force. We also give a formula for the change in the spontaneous decay rate of an excited atom or molecule near an anisotropically conducting surface.

Nuclear size effects on hydrogenic atom energies: a semi-analytic formulation

The hydrogenic energy level shifts of a Dirac lepton due to the finite size of the nucleus are developed as a double power series in nuclear/atomic size ratio R and (squared) fine structure constant α2. The method relies on matching small and large radius solutions and is much simpler than the perturbation approach of Friar (1979 Ann. Phys. 122 151). Seven terms are obtained for nS1/2, six for nP1/2 and four for nP3/2. Analytic expressions are given for the standard uniform, Gaussian and exponential models; also numerical values for various toy proton models that approximate the proton electric form factor reasonably well.

Higher order corrections to the hydrogen spectrum from the standard-model extension

We have studied the effects of the standard-model extension (SME) on hydrogen as a realization of new physics effects that incorporate Lorentz and $CPT$ violation. Specifically, we calculated the SME-induced energy level shifts at order ${\ensuremath{\alpha}}^{2}$ times the SME parameters. We obtained contributions at this order both from the nonrelativistic effective Hamiltonian for motion of a spin-$1/2$ particle in the presence of SME interactions and also from SME corrections to the propagator for exchange photons. We applied our result to the $2S\ensuremath{-}1S$ transition in hydrogen, which has been measured with extremely high precision. The results obtained in this work give the leading SME corrections for this transition.

Non-adiabatic population transfer in coupled bosonic systems

We study nonlinear Landau–Zener tunnelling in discrete Gross–Pitaevskii systems accounting for finite energy-level shifts generated by broadened pulse shapes in the non-adiabatic regime. Under these conditions, the tunnelling dynamics is generally sensitive to the pulse arrival time, however, we show that through variation of the pulse shape one can recover a case of rapid high fidelity population transfer independent of the pulse arrival time. We demonstrate how population transfer is possible in two-mode and three-mode systems. In large systems, we expect that population transfer between a pair of modes can be achieved through the application of a sequence of pulses that select pairs of neighbouring modes at each step.

XPS quantification of the hetero-junction interface energy

We present an approach for quantifying the heterogeneous interface bond energy using X-ray photoelectron spectroscopy (XPS). Firstly, from analyzing the XPS core-level shift of the elemental surfaces we obtained the energy levels of an isolated atom and their bulk shifts of the constituent elements for reference; then we measured the energy shifts of the specific energy levels upon interface alloy formation. Subtracting the referential spectrum from that collected from the alloy, we can distil the interface effect on the binding energy. Calibrated based on the energy levels and their bulk shifts derived from elemental surfaces, we can derive the bond energy, energy density, atomic cohesive energy, and free energy at the interface region. This approach has enabled us to clarify the dominance of quantum entrapment at CuPd interface and the dominance of polarization at AgPd and BeW interfaces, as the origin of interface energy change. Developed approach not only enhances the power of XPS but also enables the quantification of the interface energy at the atomic scale that has been an issue of long challenge.

Electric Field‐Induced Dipole Switching at the Donor/Acceptor Interface in Organic Solar Cells

Order of dipole moment layers at donor and acceptor interfaces in bilayer organic solar cells is manipulated reversibly by applying bias voltages. The energy level shifts at the interfaces induce reversible changes in the open circuit voltage and the diode properties. This finding could lead to a better understanding of the structure-property relationship at the materials interfaces in organic optoelectronic devices.

Relative Energy Shift of a Two-Level Atom in a Cylindrical Spacetime

We investigate the evolution dynamics of a two-level atom system interacting with the massless scalar field in a Cylindrical spacetime. We find that both the energy shifts of ground state and excited state can be separated into two parts due to the vacuum fluctuations. One is the corresponding energy shift for a rest atom in four-dimensional Minkowski space without spatial compactification, the other is just the modification of the spatial compactified periodic length. It will reveal that the influence of the presence of one spatial compactified dimension can not be neglected in Lamb shift as the relative energy level shift of an atom.

Quantum spin transport through magnetic superatom dimer (Cs8V-Cs8V)

Theoretical studies of the spin transport through a magnetic superatom dimer (Cs(8)V)-(Cs(8)V) have been carried out within a density functional theory combined with nonequilibrium Green's-function formalism. It is shown that the electronic transport is sensitive to the binding site as well as the contact distance between the dimer and the electrode, and that the conductance at zero bias exhibits an oscillatory behavior as a function of the contact distance. The conductance in ferromagnetic state shows an unusually high spin polarization that exceeds 80% at large separations. The I-V curve shows negative differential resistance for specific contact distances, whose origin lies in the shift of frontier energy levels as well as the charged state of the superatom, under external bias.

Measurement of Energy Level Shift of Ultracold Cesium Atoms by Raman Pump–Probe Spectroscopy

AC Stark shift and Zeeman shift of ultracold atoms are measured by a simple Raman pump–probe spectroscopy. We systematically investigate the relationship between these energy level shifts and the experimental parameters of trapping beam intensity, trapping beam detuning and magnetic gradient. The experimental results agree with theoretical values predicted by F ¼ 1 $ F 0 ¼ 2 model, which is developed from a multi-level cesium atom interacting

Tuning Magnetism and Electronic Phase Transitions by Strain and Electric Field in Zigzag MoS2 Nanoribbons.

Effective modulation of physical properties via external control may open various potential nanoelectronic applications of single-layer MoS2 nanoribbons (MoS2NRs). We show by first-principles calculations that the magnetic and electronic properties of zigzag MoS2NRs exhibit sensitive response to applied strain and electric field. Tensile strain in the zigzag direction produces reversible modulation of magnetic moments and electronic phase transitions among metallic, half-metallic, and semiconducting states, which stem from the energy-level shifts induced by an internal electric polarization and the competing covalent/ionic interactions. A simultaneously applied electric field further enhances or suppresses the strain-induced modulations depending on the direction of the electric field relative to the internal polarization. These findings suggest a robust and efficient approach to modulating the properties of MoS2NRs by a combination of strain engineering and electric field tuning.

Temperature dependence of the energy-level shift induced by the Bose—Einstein condensation of photons

We investigate the energy-level shift of a hydrogen atom in a two-dimensional optical microcavity, where there exists a Bose—Einstein condensation of photons. It is found that below the critical temperature Tc, the energy-level shift of the bound electron is dependent on temperature, and it is a monotonically increasing function of the absolute temperature T. Especially, at the absolute zero temperature, the energy-level shift entirely comes from the Lamb shift, and the atom can be treated approximately, that is, in vacuum.

Erratum: Multipolar theory of blackbody radiation shift of atomic energy levels and its implications for optical lattice clocks [Phys. Rev. A74, 020502(R) (2006)

Erratum: Multipolar theory of blackbody radiation shift of atomic energy levels and its implications for optical lattice clocks [Phys. Rev. A<b>74</b>, 020502(R) (2006)

Subcycle ac Stark Shift of Helium Excited States Probed with Isolated Attosecond Pulses

Recent advances in attosecond science have relied upon the nearly instantaneous response of free electrons to an external field. However, it is still not clear whether bound electrons are able to rearrange on sublaser cycle time scales. Here, we probe the optical Stark shifts induced by a few-cycle near infrared laser field in helium bound states using isolated attosecond pulses in a transient absorption scheme and uncover a subcycle laser-induced energy level shift of the laser-dressed 1s3p state.

Quantum electrodynamics near a dispersive and absorbing dielectric

We build up a consistent theory of quantum electrodynamics in the presence of macroscopic polarizable media. We use the Huttner-Barnett model of a dispersive and absorbing dielectric medium and formulate the theory in terms of interacting quantum fields. We integrate out the damped polaritons by using diagrammatic techniques and find an exact expression for the displacement field (photon) propagator in the presence of a dispersive and absorbing dielectric half-space. This opens a new route to traceable perturbative calculations of the same kind as in free-space quantum electrodynamics. As a worked-through example we consider the interaction of a neutral atom with a dispersive and absorbing dielectric half-space. For that we use the multipolar coupling $\boldsymbol{\mu}\cdot\mathbf{D}$ of the atomic dipole moment to the electromagnetic displacement field. We apply the newly developed formalism to calculate the one-loop correction to the atomic electron propagator and find the energy-level shift and changes in the spontaneous decay rates for a neutral atom close to an absorptive dielectric mirror.

Casimir—Polder-Like Force for an Atom in Hartle—Hawking Vacuum outside a Schwarzschild Black Hole

We calculate the energy level shift of a static ground state two-level atom interacting with fluctuating massless scalar fields in the Hartle-Hawking vacuum outside a Schwarzschild black hole. It is found that the energy level shift is position-dependent and gives rise to a force on the atom besides the classical gravitational force. This force behaves like r−1(r-2M)−1 for r approaching 2M, whereas it behaves like r−2 for large r.

Quantum-number–dependent energy level shifts of ions in dense plasmas: A generalized analytical approach

Dense plasma effects on bound energy levels have been studied with relativistic atomic structure simulations that include intermediate coupling and configuration interaction. A general analytical formula is proposed that predicts the energy of LSJ-split levels for wide conditions of density and finite temperature and any atomic element. The achieved precision of the analytical approach allowed even to describe energy level crossings and the breakdown of level degeneration induced by dense plasma effects. Finally, a further simplification of the proposed method is developed that requests only information on energy level energies and quantum numbers of isolated atoms that are readily available.

Naphthyl Derivatives Functionalised with Electron Acceptor Units – Synthesis, Electronic Characterisation and DFT Calculations

AbstractA series of unsymmetrical dyes containing a naphthyl unit connected to an electron acceptor moiety was designed and synthesised. By modifying the electron acceptor unit, a shift of the LUMO energy level as well as its distribution through the molecule were achieved. These dyes were fully characterised by optical, computational and electrochemical techniques. In addition, crystal structures reveal different packing depending upon the nature of the acceptor. Their potential use as electron acceptor materials for organic photovoltaics (OPVs) was also investigated by photoluminescence studies of blends with the common OPV polymers P3HT and PCDTBT.

Emergence of localized in-gap states in conjugated polymers of branched topology

Using cryogenic scanning tunneling microscopy and spectroscopy, we investigated cross-linked phenyelene-based polymers with various branched morphology at a single-molecule resolution. We found that localized states that are in the band gap of un-branched polymers emerge at the branch junctions. These in-gap states can be shifted close to the Fermi level through three means: extending the length of branch arms, coupling adjacent branches in hyperbranched structures, or increasing the number of branch arms. Single-band tight-binding calculations can reproduce all experimental results and provide quantitative relationships between the energy level shifts and the branching geometry. Our discovery evidences the emergence and development of in-gap states in the band structures of conjugated systems with fractional dimensions.

Asymmetrically Doped GaAs/AlGaAs Double-Quantum-Well Structure for Voltage-Tunable Infrared Detection

We fabricate, characterize, and analyze tunable mid-infrared photodetectors based on asymmetrically doped coupled quantum well GaAs/AlGaAs structures. The peak of photoresponse detection varies from 7.5 to 11.1 µm when switching bias from -5 to +5 V. The spectral tunability is defined by the interplay of several effects. First, the electron energy levels are shifted due to the Stark effect. Second, the applied electric field causes the charge redistribution in the coupled wells and shift of electron energy levels due to modification of self-consistent potential. Here we show that effect of electric field on tunneling processes (the Poole–Frenkel effect) and the field-induced decrease of thermo-emission barrier (the Fowler–Nordheim effect) also play a critical role in photoelectron kinetics, strongly enhancing the carrier extraction from quantum wells. The model which takes into account Poole–Frenkel and Fowler–Nordheim effects provides a quantitative description of the data obtained.