Finite Excitation Energy Research Articles

Effects of finite excitation energy of environment on fast quantum tunneling.

Quantum tunneling under the influence of an environment with nearly degenerate spectrum is considered. We first give a general derivation of the zero point motion formula in the sudden tunneling limit. The effects of a finite excitation energy of the environment are then considered by a perturbation method. Examples of linear oscillator coupling and rotational coupling show that the finite excitation energy can be represented by a dissipation factor and reduces the tunneling probability estimated in the limit of sudden tunneling. These examples clearly show that the applicability of the sudden tunneling approximation is governed by the details of the coupling as well as the relative time scales of the tunneling and the environmental degrees of freedom. We discuss some applications to heavy-ion fusion reactions.

Planck-mass-rotons cold dark matter hypothesis

Sakharov's conjecture that the vacuum is densely occupied with Planck-mass maximons is taken as a model to explain the missing mass as rotons of a superfluid made up from the Planck-mass maximons. Because rotons require a finite excitation energy, they not only can account for the missing mass but, in addition, can mimic a small, positive cosmological constant. According to Sakharov, the large vacuum energy of the Planck-mass maximons is compensated by “ghost particles.” In the proposed superfluid vacuum model, we assume that the compensation is done by a large, negative cosmological constant instead.

Electrical Properties of Heavily Be-doped GaAs grown by Molecular Beam Epitaxy

AbstractElectrical properties of heavily Be-doped GaAs grown by molecular beam epitaxy were investigated systematically in a wide range of Be-concentration from 1× 1014 up to 2× 1020 cm-3 by using yan der Pauw technique. Probable carrier scattering mechanisms observed in this work are discussed by taking into account the radiative mechanisms of several new photoluminescence emissions previously observed in the band-edge-emission region of the samples. All samples were checked their electrical properties first at room-temperature. Five selected samples out of them were measured from 10° K up to room-temperature. Samples having the carrier concentration from 1014 to 1018 cm3 presented typical semiconductor-like conduction with finite carrier excitation energy. For samples having carrier concentration 7× 1016 cm -3, the conduction mechanism at high temperature region above 30β K was dominated by holes thermally excited into valence band. At low temperature region below 30° K . it was dominated by holes hopping from neutral to ionized acceptors with the assistance of phonons. Hole mobilities of samples having the carrier concentration from 1017 to 1018 cm-3 showed an anomalous behavior in the low temperature region, which suggests the presence of a new type of carrier scattering mechanism. A radiative center denoted by lg-gl observed in this concentration region will be a candidate scattering center to explain these electrical behaviors. Samples having the carrier concentration larger than 1019 cm-3 demonstrated typically metallic electric conduction not owing to thermally excited carriers, which means that an impurity band is formed but merged with valence band. The density of state of this combined valence band mixed with impurity band can be supposed to reflect carrier concentration dependence of the PL emission bands observed in this region, i.e. [g-g]α , [g-g]β and [g-g]γ .

States of the phase-damped oscillator.

In the modeling of damped quantum systems by coupling to a heat bath, it has been usual to assume the initial factorization of the density matrix into system and bath components. For realistic couplings, this does not represent a physically reasonable state. One of the simplest such models is that of phase damping, and an alternative characterization of its initial states can be obtained exactly and without ambiguity. The consequences of these new states are particularly interesting when the system is considered as a primitive model of number measurement: The local system cannot, with a finite excitation energy, be put into a superposition of number states. This is a stronger result than from previous treatment of this system, which only showed that such superpositions would decay to mixtures. Similar conclusions can be drawn for other quantum nondemolition measurements.

Justification for the replacement of several coupled channels at a finite excitation energy by a single effective one

We clarify how a set of states at a finite excitation energy can be effectively replaced by a single state in coupled channel calculations.

Electron Spin Resonance onGaAs−AlxGa1−xAsHeterostructures

Photoconductivity measurements on $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterostructures with photon energies $0.05 \mathrm{meV}lh\ensuremath{\nu}l0.14 \mathrm{meV}$ show resonance structures with a half-width of less than 0.002 meV in the magnetic field range $3 \mathrm{T}lBl8 \mathrm{T}$. The resonances are only observed at magnetic field values where the Fermi level is located between spin-split levels and are attributed to electron spin resonance. The $g$ factor depends on the carrier density. The linear extrapolation of the resonance energy to $B=0 \mathrm{T}$ leads to a finite excitation energy.

The giant dipole resonance in hot rotating nuclei

The giant dipole resonance in deformed rotating nuclei at finite excitation energies is studied within the framework of temperature dependent linear response theory. The peak energy of the resonance and their splitting is studied as a function of angular momentum and temperature.

Interpretation of x-ray photoelectron spectra for large systems

We show that for an infinite system of noninteracting electrons the local properties of excited states with finite excitation energies are the same as for the ground state, if all one-particle states are extended. An interpretation of the x-ray photoelectron spectrum in terms of the local properties of individual eigenstates in the presence of a core hole is therefore not appropriate for an infinite system. Experimentally we can in general only study wave packets of such eigenstates, and we show how the wave packets are constructed for a particular experiment, Auger-electron---photoelectron coincidence spectroscopy. Using wave packets we can also for infinite systems introduce the concept of "screened" and "unscreened" peaks, which has an obvious meaning for small clusters of atoms.

Solitary waves in a two-dimensional diatomic lattice

Static solitary excitations in a two-dimensional diatomic lattice are studied in detail. The authors' model uses a local anharmonic electron-ion coupling for the polarisability of the anion and harmonic couplings between different chains. This lattice may serve as a model for certain ferro-electric materials. Solitary finite-energy excitations are found and proved to be stable.

Inelastic neutron scattering by coupled rotational and translational modes in KCN

The TA [100] phonon branch of the molecular crystal KCN was studied by inelastic neutron scattering in the cubic phase. In addition the distribution of the quasielastic scattered neutrons was investigated. The results are analysed by assuming a coupling of the phonon modes to the rotational degrees of freedom of the CN-dumb-bells which are regarded as a system of interacting quadrupoles. A good description of the present results and also of the existing ultrasonic and Brillouin data is achieved by a simple model which uses a single collective rotational mode of finite excitation energy and line width.

Phase transitions in quantum field theory. I. Phases of the Thirring model

In this series of papers we exhibit and analyse phase transitions in quantum field theory. In this paper we consider the Thirring model. We show that when the interaction becomes sufficiently attractive there is a transition to a vacuum that is ‘dead” in the sense there are no finite energy excitations. Nevertheless the corresponding continuum Green's functions exist. We make this demonstration precise by considering the model on a lattice and constructing the continuum limit explicitly on either side of the critical point. For this we extensively use the connection between the spin- 1 2 x-y-z chain and the lattice model. We also show a new continuum theory with four fermion interactions exists in 1 + 1 dimensions. This theory corresponds to taking the continuum limit of the spin chain in absence of any external magnetic field. Its Hamiltonian differs from that of the Thirring model by addition of fermion number operator with an infinite coefficient and is not renormalizable in the conventional sense. It has more interesting critical properties and a different spectrum.

Modified Glauber approximation for particle-atom scattering

The Glauber impact-parameter approximation for particle-atom collisions has been modified by including a finite mean excitation energy of the atom in its intermediate states.

Shell effects in a paired nucleus for finite excitation energies

Shell effects are considered as functions of the excitation energy of the nucleus. The effects of pairing are included and studied in the BCS approximation. Some numerical results, based on the single-particle spectrum of a Woods-Saxon potential, are given. In the limit of zero excitation the shell correction to the energy is compared with the results obtained by the Strutinsky method.

On the model-independent evaluation of inelastic electron scattering data at low momentum transfer

At low momentum transfer, electro-excitation experiments may be corrected for the static Coulomb effects in a model-independent way. This is demonstrated in the case of magnetic transitions for various phenomenological current and magnetization distributions. The inclusion of a finite excitation energy gives mainly a kinematical effect. It is further shown that for transverse transitions the notion of a “transition radius” has no model-independent physical meaning and should be avoided.