首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
The excitonic representation method for describing collective excitations in the quantized Hall regime makes it possible to simplify analysis of the spectra and to obtain new results in the strong magnetic field limit, when E C ??ωcc is the cyclotron frequency and EC is the characteristic Coulomb energy). For an integer odd filling factor ν greater than unity (i.e., for ν = 3, 5, 7,...), the spectra of one-cyclotron magneto-plasma excitations are calculated. For unit filling factor, the existence of a spin biexciton (bound state of two spin waves) corresponding to excitation with a spin change (δS = δSz = ?2) is proved. The exact equation determining the ground state of the biexciton is derived in the thermodynamic limit NΦ → ∞ (N? is the system degeneracy). The exchange energy of this state is lower than for a single spin wave (with δS = δSz = ?1) for the same value of the 2D wavevector q. In the limit q → ∞ corresponding to the decay of a biexciton into a pair of quasiparticles one of which is a trion with a spin of ?3/2, the energy is found to be lower than the energy (e2/εl B )√π/2 required for exciting an electron-hole pair in the strictly 2D case (lB is the magnetic length and ε is the dielectric constant), although this energy is higher than another “classical” result (e2/εl B )√π/2, corresponding to the excitation of a skyrmion-antiskyrmion pair (|δS|=|δS z |?1). The solution of the exact equation gives the trion binding energy and the activation gap for quasiparticles whose excitation corresponds to a change in the total spin by δS = δ Sz =?3. The energy of a spin biexciton is calculated for values of the wavevector such that ql B ?1.  相似文献   

2.
The energy dependence of the proton polarizationP has been measured for a fixed reaction angle of 52 degrees by p-He4 elastic scattering.P varies rapidly with the deuteron energyE d . The experimental results are in good agreement with the assumption of aJ π = 1? level of the compound nucleus N14 at 11,23 MeV (E d = 1,13 MeV).  相似文献   

3.
Spin excitations in granular structures with ferromagnetic nanoparticles   总被引:1,自引:0,他引:1  
Spin excitations and relaxation in a granular structure which contains metallic ferromagnetic nanoparticles in an insulating amorphous matrix are studied in the framework of the s-d exchange model. As the d system, we consider the granule spins, and the s system is represented by localized electrons in the amorphous matrix. In the one-loop approximation with respect to the s-d exchange interaction for a diagram expansion of the spin Green’s function, the spin excitation spectrum is found, which consists of spin-wave excitations in the granules and of polarized spin excitations. In polarized spin excitations, a change in the granule spin direction is accompanied by an electron transition with a spin flip between two sublevels of a split localized state in the matrix. We considered polarized spin relaxation (relaxation of the granule spins occurring by means of polarized spin excitations) determined by localized deep energy states in the matrix and the thermally activated electronic cloud of the granule. It is found that polarized spin relaxation is efficient over a wide frequency range. Estimates made for structures with cobalt granules showed that this relaxation could be observed in centimetric, millimetric, and submillimetric wavelength ranges.  相似文献   

4.
The instability of nuclear matter is considered for the case where it is generated by the vanishing of the frequencies of collective excitations belonging to specific types (specifically, excitations that have the pion quantum numbers J π = 0?). The behavior of zero-frequency solutions to the pion dispersion equation is analyzed versus the strength G′ of spin—isospin particle—hole interaction. It is shown that there exists a strength value Gtr (|Gtr| ? 1) such that, for G′ < Gtr, zero-frequency solutions are excitations of the ω P type, while, for G′ ≥ Gtr, such solutions are excitations of the ω c type. Excitations of the ω P type for G′ < ?1 describe the instability of nuclear matter against small density fluctuations (Pomeranchuk’s instability), while excitations of the ω c type are responsible for the instability associated with pion condensation at G′ ≈ 2. For stable nuclear matter, the solutions ω P(κ) and ω c (κ) lie on unphysical sheets of the complex plane of frequency.  相似文献   

5.
The energy of plasma oscillations of free charge carriers in bismuth crystals ?ωp can be qual to the band gap at the L point of the Brillouin zone E gL as a result of doping with an acceptor impurity. Variation in the edge shape and splitting of the minimum in the plasma reflection are observed in experimental studies of reflection under normal incidence of radiation on the crystal. An analysis of the totality of available experimental data shows that the above special features are caused by interaction of elementary excitations (such as the plasma oscillations) with band-to-band transitions. It became possible for the first time to ascertain the composition of the bismuth crystals for which the condition ?ωp=E gL is satisfied and observe the variation in the characteristics of the plasma oscillations of free charge carriers, which occurs as a result of electron-plasmon interaction.  相似文献   

6.
A microcanonical distribution function depending on the total energyE and thez-componentM of the total angular momentum of a rotating system is examined. ForM=0 the generalized microcanonical ensemble is found to give the same entropy as the usual microcanonical ensemble. The moment of inertia of a rotating gas is calculated, and the kinetic energy of rotation is given as a power series in the small parameterM 2/2I 0Eint, whereI 0 is the moment of inertia of the gas at rest andE int the internal energy.  相似文献   

7.
Electron spin resonance linewidths of ions belonging to the first transition group with quenched orbital angular momentum are calculated using a modified relaxationmatrix theory including third and fourth order perturbation terms. We base our calculation on a Hamiltonian, which depends on electron spin, nuclear spin, orbital angular momentum, rotation of the whole complex, and vibration of the ligands. Quadrupol effects, intermolecular electron-electron and electron-nucleus interactions are neglected. The results show that the well-known formula of the transverse relaxation time derived by using the spin-Hamiltonian is correct, if first the contribution of the rotational spin orbit process is taken in consideration and second the rotational correlation timeτ c is replaced byτ v =(1/τ c +1/τ(0))?1. 1/τ(0) describes the linewidth of the lowest energy value of the electrostatic energy of unpaired electrons in the ligand field. The linewidth arises from the normal modes of the complex; the calculation gives τ(0)=l0?11...10?12 sec.  相似文献   

8.
9.
A system of particles with spin in a magnetic field may possess an orbital temperatureT o different from the spin temperatureT s (?0), if it is possible to neglect the energetic interaction between the orbital and the spin system. The calculation of the quantum statistical most probable distribution of identical independent particles on the orbital and spin energy levels yields the introduction of three Lagrange multipliers—according to the fact that the orbital and the spin energy and the number of particles are fixed—representing the orbital and spin temperature and a generalizedPlanck's “characteristic function”. Apart from the Boltzmann-approximation being valid in the case of small spin values forT o ?T e (T e =customary degeneration temperature) and arbitraryT s ?0, the distributions and the orbital and the spin energy depend onboth the temperaturesT o andT s coming from the principle of exclusion forFermi resp.Bose particles. The equations of state are discussed. There are four heat capacities, which possess characteristic peaks. In stead of the well-known temperature independence of the paramagnetism of degenerated conducting electrons one obtains χ~T o /T s . The behaviour of the Einstein-condensation of aBose gas is considered.  相似文献   

10.
11.
The first 2+ states in N=20 isotones are studied within the self-consistent quasiparticle random phase approximation based on the Green’s function method. The residual interaction between quasiparticles with full velocity dependence is consistently derived from the Skyrme interaction plus pairing interaction energy density functional. The B(E2, 0 1 + → 2 1 + ) transition probabilities and the excitation energies of the first 2+ states are well described within a single framework. We discuss mainly the microscopic origin of the anomalously large B(E2) value and the very low excitation energy in 32Mg.  相似文献   

12.
For a two-dimensional Heisenberg ferromagnet, a class of steady-state nonlinear excitations above the ground state is considered. The excitations have the form of stripes and exhibit quasiparticle properties. The effect of an external magnetic field on the basic characteristics of these nonlinear topological excitations is investigated. The magnetic field is found to destroy the instanton-type solutions (kinks) and to generate new particles with the properties of vortex-antivortex pairs: each particle has a zero topological charge and an energy close to the double skyrmion energy 8πJS2. The dispersion of the quasiparticles and the dependences of their energy and momentum on the number of magnons localized by one excitation are discussed.  相似文献   

13.
The temperature correction to the free energy of the gravitational field is considered which does not depend on the Planck energy physics. The leading correction may be interpreted in terms of the temperature-dependent effective gravitational constant Geff. The temperature correction to appears to be valid for all temperatures T?EPlanck. It is universal since it is determined only by the number of fermionic and bosonic fields with masses m?T, does not contain the Planck energy scale EPlanck which determines the gravitational constant at T=0, and does not depend on whether or not the gravitational field obeys the Einstein equations. That is why this universal modification of the free energy for gravitational field can be used to study thermodynamics of quantum systems in condensed matter (such as quantum liquids superfluid 3He and 4He), where the effective gravity emerging for fermionic and/or bosonic quasiparticles in the low-energy corner is quite different from the Einstein gravity.  相似文献   

14.
Corrections of order α 5 and α 6 are calculated for muonic hydrogen in the fine-structure interval ΔE fs = E(2P 3/2) − E(2P 1/2) and in the hyperfine structure of the 2P 1/2-and 2P 3/2-wave energy levels. The resulting values of ΔE fs = 8352.08 μeV, Δ hfs(2P 1/2) = 7819.80 μeV, and Δ hfs(2P 3/2) = 3248.03 μeV provide reliable guidelines in performing a comparison with relevant experimental data and in more precisely extracting the experimental value of the (2P–2S) Lamb shift in the muonic-hydrogen atom. Original Russian Text ? A.P. Martynenko, 2008, published in Yadernaya Fizika, 2008, Vol. 71, No. 1, pp. 126–136.  相似文献   

15.
Photoproductions of single pions for high energies and small momentum transfer is considered. The production amplitude is approximated by exchange ofρ-,ω-,?- andπ-meson in the crossed chanellγ+πN+¯N. These mesons are treated either as “elementary” or as Regge poles. The angular distribution is caclulated in the high energy limit and discussed in detail.  相似文献   

16.
The short lived indium isomer produced by thermal neutron capture is confirmed to be In116. A new determination of half-live andγ energy yieldsT 1/2=(2.17α0.07) sec andE γ=(164±1) keV. From measurement of theK shell conversion coefficient follows that the multipolarity of the transition isE 3, leading to a spin and parity assignment of 8? for the isomeric level.  相似文献   

17.
The results of a partial-wave analysis of the angular distributions for the process γpηp over the energy range up to 2 GeV are presented. Reliable estimates of the Breit-Wigner parameters of the S11(1535) resonance, as well as the energy dependence of the real and imaginary parts of the electric dipole amplitude E0+ and its phase, are derived from the energy dependence of the regression coefficient a0(W).  相似文献   

18.
The T-invariance condition was analyzed for the amplitude T b,a of multiparticle multistep elastic or inelastic ab nuclear reactions. This condition leads to the equality of the amplitude T b,a to the amplitude \({\tilde T_{\bar a,\bar b}}\) of \(\bar b \to \bar a\) time-reversed reaction, for which the reaction operator \(\tilde T\) coincides with the inverse-reaction (ba) operator. It is shown that, in the case where the original, inverse, and time-reversed reactions are governed by a common T-invariant mechanism, the coefficients D of asymmetries appearing in the differential cross sections for these reactions can be represented in the form of a unified scalar (pseudoscalar) function of arguments equal to the momentum and spin vectors of particles of the initial and final channels of the reactions under analysis. It is also shown that the use of the T-invariance condition for the coefficients D of asymmetries in the differential cross section for the original nuclear reaction that are different in P- and T-parity makes it possible to separate mechanisms leading to nonzero coefficients D for a number of the asymmetries under analysis from the remaining mechanisms leading to zero coefficients D of these asymmetries. It is proven that there exist such asymmetries in the differential cross section for the original reaction whose coefficients vanish for all possible T-invariant mechanisms of their appearance, so that, upon proving experimentally the appearance of nonzero coefficients of these asymmetries in the differential cross section for the original reaction, this fact can be used to assess features of T-noninvariant interactions in nuclear systems.  相似文献   

19.
The elastic-scattering process proceeding through two resonance levels that have the same spin j and equal resonance energies, (E1 = E2), but different widths (Γ1 ≠ Γ2) is considered. It is shown that the energy dependence of the total scattering cross section has two equal maxima at the points E1 ± (1/2) \(\sqrt {{\Gamma _1}{\Gamma _2}} \), the cross-section value at the maxima being 4π (2j + 1)?2, where ? is the wavelength of the incident particle in the c.m. frame, and that, at the energy E1, the cross section vanishes, σ (E1) = 0. The cross section is symmetric with respect to the point E1.  相似文献   

20.
A method for calculating electric quadrupole moments of light nuclei and probabilities of electric quadrupole transitions in them in the multiquantum approximation of the orthogonal scheme is proposed. Specific calculations of these quantities are performed for the 4 8 Be nucleus with allowance for all U(3(A ? 1)) states characterized by the λ = [44] Young diagram, the quantum numbers K min and K min + 2 of the O(3A ? 1)) group, and the number E = K + 2N (N = 0, 1, …, 9) of oscillator quanta. It is shown that an extension of the basis from the E = K min to the E = K min + 2 approximation leads to an increase of 15 to 45% in the electric quadrupole moments and to an increase in the transition probabilities B(E2) by a factor of 1.6 to 2.8. The inclusion of E = K + 2N (N = 0, 1, …), states involving multiquantum excitations (ρ excitations) increases additionally the results by 10 to 30%. The results of these calculations are compared with their counterparts obtained in the multiquantum approximation of the unitary scheme.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号