共查询到20条相似文献,搜索用时 31 毫秒
1.
We report a detailed theoretical study of the effect of combined electric and magnetic field on the nonlinear optical rectification of a hydrogenic impurity, confined in a two dimensional disk-like quantum dot, with parabolic confinement potential. We use the compact density matrix formalism and iterative method to obtain nonlinear optical rectification and absorption coefficients. To find energy levels and wave functions, we employ exact diagonalization method in the effective mass approximation. As main result, we found that the transition energy from ground to first excited state redshifts with increasing the magnetic field while blueshifts for transition from ground to second excited state, moreover, for former transition, nonlinear optical rectification coefficient decreases with increasing magnetic field in contrast to that occurs for latter one. 相似文献
2.
Reliable predictions for jet quenching in ultra-relativistic heavy ion collisions require accurate computation of radiative energy loss. While all available energy loss formalisms assume zero magnetic mass – in accordance with the one-loop perturbative calculations – different non-perturbative approaches report a non-zero magnetic mass at RHIC and LHC. We here generalize a recently developed energy loss formalism in a realistic finite size QCD medium, to consistently include a possibility for existence of non-zero magnetic screening. We also present how the inclusion of finite magnetic mass changes the energy loss results. Our analysis suggests a fundamental constraint on magnetic to electric mass ratio. 相似文献
3.
We present a semi-analytic study of Ising spins on a simple square or
cubic lattice coupled to a transverse
magnetic field of variable strength. The formal analysis employs
correlated basis functions (CBF) theory to
investigate the properties of the corresponding N-body ground and
excited states. For these states we discuss
two different ansaetze of correlated trial wave functions and associated
longitudinal and transverse excitation
modes. The formalism is then generalized to describe the spin system at
nonzero temperatures with the help of
a suitable functional approximating the Helmholtz free energy. To test
the quality of the functional in a first step
we perform numerical calculations within the extended formalism but
ignore spatial correlations. Numerical results are
reported on the energies of the longitudinal and the transverse
excitation modes at zero temperature, on critical
data at finite temperatures, and on the optimized spontaneous
magnetization as a function of temperature and
external field strength. 相似文献
4.
C. Haupt B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2006,28(2):213-225
We show that static properties like the charge radius and the magnetic moment of relativistic three-fermion bound states with
instantaneous interactions can be formulated as expectation values with respect to intrinsically defined wave functions. The
resulting operators can be given a natural physical interpretation in accordance with relativistic covariance. We also indicate
how the formalism may be generalized to arbitrary moments. The method is applied to the computation of static baryon properties
with numerical results for the nucleon charge radii and the baryon octet magnetic moments. In addition, we make predictions
for the magnetic moments of some selected nucleon resonances and discuss the decomposition of the nucleon magnetic moments
in contributions of spin and angular momentum, as well as the evolution of these contributions with decreasing quark mass. 相似文献
5.
Photon can mix with the axion-like particles (ALPs) on light polarization when the laser beam travels through a magnetic field.
Since there is no conclusive evidence of an exact zero rest mass for the photon in various experiments and observations, we
study the Proca effects in various ALP-photon regeneration experiments and develop a formalism which can be adopted to study
the evolution of a massive photon in the presence of external magnetic fields. We find that the Proca effects are much smaller
than the effects of the standard QCD axions. But if the masses of such particles are comparable, the Proca effects can not
be neglected. Furthermore, we get the implied photon mass limit and discuss the feasibility of extending the search for the
photon mass limit in this area. 相似文献
6.
M.A. Itskovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):283-296
Theory of magnetoquantum oscillations with spin-split structure in strongly anisotropic (two-dimensional (2D)) metal is developed
in the formalism of level approach. Parametric method for exact calculation of oscillations wave forms and amplitudes, developed
earlier for spin degenerate levels is generalized on a 2D electron system with spin-split levels. General results are proved:
1) proportionality relation between magnetization and chemical potential oscillations accounting for spin-split energy levels
and magnetic field unperturbed levels (states of reservoir), 2) basic equation for chemical potential oscillations invariant
to various models of 2D and 1D energy bands (intersecting or overlapping) and localized states. Equilibrium transfer of carriers
between overlapping 2D and 1D bands, characterizing the band structure of organic quasi 2D metals, is considered. Transfer
parameter, calculated in this model to be of the order of unity, confirms the fact that the wave form of oscillations in organic metals should be quasisymmetric up to ultralow temperature. Presented theory accounts for spin-split magnetization oscillations at magnetic field directions tilted relative to the anisotropic
axis of a metal. Theoretical results are compared with available experimental data on organic quasi-2D metal α-(BEDT-TTF)2KHg(SNC)4 explaining the appearance of clear split structure under the kink magnetic field and absence above by the corresponding change
in the electron g-factor rather than cyclotron mass.
Received 20 December 2000 and Received in final form 13 July 2001 相似文献
7.
M.N. Kiselev H. Feldmann R. Oppermann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):53-63
We represent the generators of the SU(N) algebra as bilinear combinations of Fermi operators with imaginary chemical potential. The distribution function, consisting
of a minimal set of discrete imaginary chemical potentials, is introduced to satisfy the local constraints. This representation
leads to the conventional temperature diagram technique with standard Feynman codex, except that the Matsubara frequencies
are determined by neither integer nor half-integer numbers. The real-time Schwinger-Keldysh formalism is formulated in the
framework of complex equilibrium distribution functions for auxiliary semi-fermionic fields. We discuss the continuous large
N and SU(2) large spin limits. We illustrate the application of this technique for magnetic and spin-liquid states of the Heisenberg
model.
Received 26 February 2001 and Received in final form 25 April 2001 相似文献
8.
B.S. Kandemir T. Altanhan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):517-526
We investigate the stability condition of large bipolarons confined in a parabolic potential containing certain parameters
and a uniform magnetic field. The variational wave function is constructed as a product form of electronic parts, consisting
of center of mass and internal motion, and a part of coherent phonons generated by Lee-Low-Pines transformation from the vacuum.
An analytical expression for the bipolaron energy is found, from which the ground and excited-state energies are obtained
numerically by minimization procedure. The bipolaron stability region is determined by comparing the bipolaron energy with
those of two separate polarons, which is already calculated within the same approximation. It is shown that the results obtained
for the ground state energy of bipolarons reduce to the existing works in zero magnetic field. In the presence of a magnetic
field, the stability of bipolarons is examined, for three types of low-dimensional system, as function of certain parameters,
such as the magnetic-field, the electron-phonon coupling constant, Coulomb repulsion and the confinement strength. Numerical
solutions for the energy levels of the ground and first excited states are examined as functions of the same parameters.
Received 7 March 2002 and Received in final form 22 April 2002 Published online 25 June 2002 相似文献
9.
A. Çetin 《Physics letters. A》2008,372(21):3852-3856
We investigate the energy spectrum and the corresponding wave functions of an electron confined by a pseudoharmonic potential both including harmonic dot and antidot potentials in the presence of a strong magnetic field together with an Aharonov-Bohm flux field. Exact solutions for the energy levels and wave functions are found for this exactly soluble system. These are all tested under various conditions and also are compared with other works found in the literature. Further, we discuss the related energy spectrum in terms of special values of the proposed pseudoharmonic potential, AB field and magnetic field as a function of magnetic quantum number and magnetic field. 相似文献
10.
We here investigate the density and temperature dependence of polarization using the relativistic formalism for the electron–electron
interaction within the Fermi liquid model. The variational method has been used: the free energy has been minimized with respect
to the effective mass and the polarization parameter. Then we obtained the equation of state and magnetic susceptibility of
the system. The exact results for polarization and magnetic susceptibility have been obtained at zero temperature. It has
been shown that for a given temperature (density) there is a critical density (temperature) at which the ferromagnetic phase
can appear in an electron gas. The results are in agreement with previous work. Our results show that at nonzero temperatures
and in very low and very high densities the ferromagnetism phase cannot exist. 相似文献
11.
V. Chandra A. Ranjan V. Ravishankar 《The European Physical Journal A - Hadrons and Nuclei》2009,40(1):109-117
We study the response functions (chromo-electric susceptibilities) for an interacting quark-gluon plasma. The interaction
effects have been encoded in the effective fugacities for quasi-partons which are extracted self-consistently from the two
equations of state for hot QCD. The first one is the fully perturbative O(g
5) EOS and the second one, which is O(g
6ln(1/g)) , incorporates some non-perturbative effects. We find that the response function shows large deviations from the ideal
behavior. We further determine the temperature dependence of the Debye mass by fixing the effective coupling constant Q2 which appears in the transport equation. We show that our formalism naturally yields the leading-order HTL expression for
the Debye mass if we employ the ideal EOS. Employing the Debye mass, we estimate the dissociation temperatures for various
charmonium and bottomonium bound states. These results are consistent with the current theoretical studies. 相似文献
12.
Dirac-Maxwell equations with magnetic monopoles are generalized to electromagnetic fields by introducing fourth components
to the fields and their solutions are obtained. The formalism is presented into tensor, dyonic as well as quaternionic forms
and conservation theorems for the field energy and momenta are obtained involving the new contribution from the mutual interaction
of the fields and currents. The generation of the standard modeste, tm andtem ofem waves is also obtained in the formalism. 相似文献
13.
14.
15.
We derive an expression for the effectivegravitational mass for any closed spacelike 2-surface.This effective gravitational energy is defined directlythrough the geometrical quantity of the freely falling 2-surface and thus is well adapted to intuitiveexpectation that the gravitational mass should bedetermined by the motion of a test body moving freely inthe gravitational field. We find that this effective gravitational mass has a reasonable positivevalue for a small sphere in the non-vacuum space-timesand can be negative for the vacuum case. Further, thiseffective gravitational energy is compared with the quasi-local energy based on the (2 + 2)formalism of General Relativity. Although some gaugefreedoms exist, analytic expressions of the quasi-localenergy for vacuum cases are the same as the effective gravitational mass. Especially, we see that thecontribution from the cosmological constant is the samein general cases. 相似文献
16.
We draw motivation from recent experimental studies and present a comprehensive study of magnetothermoelectric transport in a graphene monolayer within the linear response regime. We employ the modified Kubo formalism developed for thermal transport in a magnetic field. Thermopower as well as thermal conductivity as a function of the gate voltage of a graphene monolayer in the presence of a magnetic field perpendicular to the graphene plane is determined for low magnetic fields (~1 T) as well as high fields (~8 T). We include the effects of screened charged impurities on thermal transport. We find good qualitative and quantitative agreement with recent experimental work on the subject. In addition, in order to analyze the effects of modulation, which can be induced by various means, on the thermal transport in graphene, we evaluate the thermal transport coefficients for a graphene monolayer subjected to a periodic electric modulation in a magnetic field. The results are presented as a function of the magnetic field and the gate voltage. 相似文献
17.
The nonadiabatic Berry phases in the magnetic resonance under .various initial conditions are investigated and compared with ,the adiabatic Berry phase. The generaJ formalism for calculating the nonadiabatic Berry phase of a two-state system in terpls of the expansion of instantaneous energy eigenstates is presented. Some numerical calculations and discussions are made. The Berry phase of a two-statesystem under an impulsive interaction is addressed. 相似文献
18.
A formalism is presented for extracting diffusion coefficients from concentration profiles measured by analytical techniques such as Auger electron spectroscopy, secondary ion mass spectrometry, low energy and high energy ion scattering. The formalism is based on the measurement of the concentration profile or gradient (dC/dx) at the interface before and after diffusion, and corrects for extraneous effects in the profile due to sputtering artifacts, initial diffusion, and interface and surface roughness. The formalism is shown to be quite insensitive to surface depletion caused by preferential sputtering. The process of correction involves a deconvolution which is valid for all compositions if the above effects can be represented by complementary error functions, as judged by the linearity on a “probability” plot of C versus x where C is concentration and x is distance in angstroms. The formalism is expressed in the form of a nomograph for the routine determination of diffusion coefficients from measured profiles. Examples of its use are given for profiles measured on the Ti-Pd, Ti-Au, Pd-Au, and Cu-Au thin film systems. 相似文献
19.
The formalism developed earlier by us for the propagation of a resonance in the nuclear medium in proton-nucleus collisions
has been modified to the case of vector boson production in heavy-ion collisions. The formalism includes coherently the contribution
to the observed di-lepton production from the decay of a vector boson inside as well as outside the nuclear medium. The medium
modification of the boson is incorporated through an energy dependent optical potential. The calculated invariant ρ mass distributions are presented for the ρ-meson production using optical potentials estimated within the VDM and the resonance model. The shift in the invariant mass
distribution is found to be small. To achieve the mass shift (of about 200 MeV towards lower mass) as indicated in the high
energy heavy-ion collision experiments, an unusually strong optical potential of about −120 MeV is required. We also observe
that, for not so heavy nuclear systems and/or for fast moving resonances, the shape, magnitude and peak position of the invariant
mass distribution is substantially different if the contributions from the resonance decay inside and outside are summed-up
at the amplitude level (coherently) or at the cross section level (incoherently). 相似文献
20.
We report on a theoretical study of spin-polarized quantum transport through a Ni-bezenedithiol(BDT)-Ni molecular magnetic tunnel junction (MTJ). Our study is based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism, so that microscopic details of the molecular MTJ are taken into account from first principles. A magnetoresistance ratio of approximately 27% is found for the Ni-BDT-Ni MTJ which declines toward zero as bias voltage is increased. The spin currents are nonlinear functions of bias voltage, even changing sign at certain voltages due to specific features of the coupling between molecular states and magnetic leads. 相似文献