Ferromagnetic resonance in media with an inhomogeneous saturation magnetization

The method of transition probabilities is used to calculate the line width of ferromagnetic resonance in a medium with an inhomogeneous saturation magnetization. It is shown that in addition to linear (with respect to the Fourier components of the function describing inhomogeneities) terms, the perturbation Hamiltonian must include also quadratic terms. The frequency dependence of the contribution of the porosity to H is fundamentally different from the frequency dependence of the magnetic anisotropy contribution. This anisotropy contribution H_a() decreases on increase in the frequency and has a maximum at = (2/3)_M, whereas the porosity contribution H_p increases on increase in the frequency and vanishes at = (2/3)_M.deceasedTranslated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp.48–52, December, 1980.     

Normal mode configuration in an inorganic medium containing defects

The vibrational structure in an inorganic medium containing defects is analyzed as a function of the frequency of the applied field. Since the dispersion relations for the medium are nonlinear, the configuration of the normal modes depends differently upon and . It is shown that exponential damping of the optic branches is observed for <₀, and that the structure of these modes changes significantly over the range 0<<₀, so that only in the neighborhood of ₀ does it correspond to long wavelength vibrations with configurations of stress deviator waves.Institute for the Physics of Strength and Materials Science, Russian Academy of Sciences, Siberian Division. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 87–90, October, 1994.     

Quantum antiferromagnetism in 2 dimensions

We study the spin dynamics of the 2-dimensional spin 1/2 Heisenberg model at finite temperatureT, in particular the frequency region <TJ (the coupling constant). The main conclusion reached is that the spin fluctuations have relaxational character, no propagating spin waves exist for <T. Comparison with experimental results on La₂CuO₄ give good agreement. Similarities and differences to previous theoretical treatments are discussed.     

Pulsed NMRON oscillatory free induction decay signals in the angular distribution of gamma radiation from plated60CoFe

Results for an inhomogeneously broadened⁶⁰CoFe NMRON sample have been obtained for gamma detected single pulse (nutation) and two pulse (free induction decay) experiments in the region of intermediate-to-lowR(=₁/). Here ₁ is the angular frequency measure of the strength of the ferromagnetically enhanced RF field at the nucleus and is the HWHM of the inhomogeneously broadened line. Comparisons of the oscillatory FID signals obtained are made with the theoretical predictions of the following paper [6].     

Linear and non-linear ac response of the stochastic classical model for sliding charge density waves

A comprehensive study of the ac response properties of the classical stochastic model for sliding charge density waves (CDW) in quasi one-dimensional metals is made by numerically solving the associated Fokker-Planck equation. Above the conductivity threshold a noise mechanism is indispensable to give finite line widths to the resonances of the applied ac signal of frequency with the narrow band noise frequency _OSC inherent in the model. In the present investigation a current noise of strengthT _N proportional to the CDW current is used in the Fokker-Planck equation in order to model the broad band current noise frequently observed above threshold. The present model thus incorporates three characteristic frequency scales: _OSC,T _N ,and a crossover frequency _OSC. Results are evaluated for the ac conductivity (;E ₀,E ) as function of frequency , dc bias electric fieldE ₀ and ac signal field strengthE . ForE 0 the linear ac response is obtained by a separate treatment of the Fokker-Planck equation. The resonances near =_OSC are studied in detail. Strong ac signals reduce the response at the fundamental resonance and lead to a harmonic interference structure nearn=_OSC. The overall agreement of the present results with recent measurements of the linear ac response is not good. In reality our results seem to be superimposed on a background not reproduced by the classical model with one cross over frequency. However, the peak in Im (;E ₀,E =0) vs.E ₀, when the narrow band noise frequency is near , is well reproduced. The spectral width of this peak which corresponds to the inductive dip in the susceptibility is studied as function of current noise strengthT _N .The results stress the need for a complete Fokker-Planck treatment sinceT _N is not simply related to the line width.     

The third-order electric susceptibilities of NaCl and KCl monocrystals

The dispersion of the third-order electric susceptibilities(; , , –) and(; , 0, 0) of NaCl and KCl monocrystals has been calculated by means of experimental data on the electro-optic Kerr effect. The result has been obtained by using semi-classical models of anharmonic oscillators. An ionic contribution to the electro-optic coefficients has been presented. From the result obtained it follows that the third-order electric susceptibilities are of the order of 10^–22 m² V^–2.     

Buildup of a narrow plasma channel by microwaves

The paper deals with the effect of the buildup of a narrow plasma channel by a hf right-hand circularly polarized (RHCP) wave propagating through radially inhomogeneous plasma in the direction of the static magnetic field. The plasma channel occurs under conditions when the linear transformation of the RHCP wave takes place. The experiments were carried out in a homogeneous static magnetic field _ce /2.3;, _ce are the frequency of the RHCP wave and the electron cyclotron frequency, respectively.Nademlýnská 600, Praha 9, Czechoslovakia.     

The modular group and super-KMS functionals

Every normal, faithful, self-adjoint functional on a von Neumann algebraA canonically determines a one-parameter-weakly continuous *-automorphism group (the analog of the modular group) and a canonical ₂ grading onA, commuting with . We show that the functional satisfies the weak super-KMS property with respect to and Furthermore, we prove that and are the unique pair of a-weakly continuous one-parameter *-automorphism group and a grading of the algebra, commuting with each other, with respect to which is weakly super-KMS. The above results thus provide a complete extension of the theory of Tomita and Takesaki to the nonpositive case.Supported in part by the National Science Foundation under Grant DMS-8922002.     

Cluster Structure of Collapsing Polymers

In order to better understand the geometry of the polymer collapse transition, we study the distribution of geometric clusters made up of the nearest neighbor interactions of an interacting self-avoiding walk. We argue for this new correlated percolation problem that in two dimensions, and possibly also in three dimensions, a percolation transition takes place at a temperature lower than the collapse transition. Hence this novel transition should be governed by exponents unrelated to the -point exponents. This also implies that there is a temperature range in which the polymer has collapsed, but has no long-range cluster structure. We use Monte Carlo to study the distribution of clusters on the simple cubic and Manhattan lattices. On the Manhattan lattice, where the data are most convincing, we find that the percolation transition occurs at _p =1.461(3), while the collapse transition is known to occur exactly at =1.414.... We propose a finite-size scaling form for the cluster distribution and estimate several of the critical exponents. Regardless of the value of _p , this percolation problem sheds new light on polymer collapse.     

Averaged electron Green function and CDW pinning in one-dimensional random potential

The averaged retarded electron Green functionG ⁺(,k) in 1d disordered metal is calculated using the Berezinsky diagram technique. Using the Gorkov's theory it is shown, that the substitution of inG ⁺ (,k) by the square of the external frequency atk=0 gives the dependence of Fröhlich conductivity _F(). This dependence describes the impurity pinning of CDW in 1d disordered metals. The good agreement of this dependence with experimental data Zeller et al. about _F() in quasi-1d conductor KCP is found     

Plasma instability in a strong,circularly polarized electromagnetic wave

Conclusions In summary, we have studied the parametric instability of a cold electron plasma in a strong, circularly polarized electromagnetic wave, taking into account the relativistic nature of the electron motion. We have shown that an instability of longitudinal waves occurs at frequencies _p/ and _p/, while an instability of transverse waves occurs at frequencies ₀±₀ and ₀±_p/. The results of a numerical solution of the dispersion relation for large pump amplitudes, in which case the approximation of a weak coupling between waves is not applicable, show that the growth rates and the bands of the instabilities increase with increasing pump amplitude. We have found that in the case of the excitation of electromagnetic plasma waves, even at low pump amplitudes, the relativistic nature of the electron motion can be of decisive importance for the effect.T. G. Shevchenko Kiev State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 19, No. 10, pp. 1481–1488, October, 1976.     

The Transit Time Effect of a Modulated Electron Beam

Energy change of an electron beam is studied numerically when it transits a rf field gap of width L. For a premodulated beam, the transit time L/0> for maximum energy extraction is shortened to 0.475 T (T=2/, 0> is the average velocity of the electrons) when the modulation frequency _m is matched to the rf field frequency . Enhancement of the extraction efficiency _o is dependent on the modulation coefficient h₁ and h₂. For a uniform beam with V=500 kV, _o is less than 2%. _o reaches 11% for a prebunched beam with h₁=0.7 and h₂=0.1 and will surpass 20% for an ideally modulated beam.     

Spectral superbroadening of self-focused picosecond laser pulses in D2O

Intense picosecond light pulses of a mode-locked Nd: glass laser at _L =1054 nm (fundamental wavelength) and _SH =527 nm (second harmonic wavelength) are passed through a sample of D₂O under self-focusing conditions. Spectrally structured superbroadened, spatially bell-shaped emission in the forward direction is obtained. Primary generation processes are pump-pulse-degenerate stimulated parametric four-photon interaction (₁ + _{1 3} + ₄) and stimulated Raman scattering (_{1 R} + ), which occur concurrently (₁= _L or _SH angular pump frequency, #x03C9; _R first Stokes frequency, #x03C9; signal frequency, #x03C9;₃ signal frequency, #x03C9;₄ idler frequency). The parametric four-photon interaction occurs under collinear non-phase-matched conditions and under longitudinally phase-matched, transversally non-phase-matched (erenkov-like) conditions. Subsequent interaction processes are pump-pulse-nondegenerate four-photon interaction of the type ₁ + _{R 3} + ₄, coherent antiStokes Raman scattering (CARS, ₁ + ₁ – _{4 3}), inverse Raman scattering ( _A + ₁ + ), and cascading light up-conversion of the type ₁ + _(i) – _{R (i+1)}.     

Third order nonlinear optical difference frequency generation in KH2PO4, TiO2, LiNbO3, CaCO3, ZnO and CdS

Third-order nonlinear optical susceptibilities of different crystals have been measured relative to LiNbO₃ by observing collinear phase-matched difference frequency generation ₁=2 ₂– ₄. The two incident light waves have been produced by a ruby laser ( ₂, ₂=694.3 nm) and by induced Raman scattering ( ₄, ₄=765.8 nm). With noncollinear phase-matching the number of nonlinear processes and the possibilities to determine nonlinear coefficients is much larger than in the collinear case. Therefore the theory of Raman-type third order interactions has been extended to noncollinear propagation of the interacting waves. The theory has been tested experimentally for CdS.     

Subharmonic electromagnetic radiation from cavitons

In a high-power microwave-plasma system, it has been experimentally found that electromagnetic (em) radiation at subharmonic frequencies [specifically, (3/2)₀ and (5/2)₀] of the electron plasma frequency of the unperturbed state, ₀, can be emanated from cavitons which are resonantly driven by an intense em pulse (frequency ₀) in an unmagnetized inhomogeneous plasma. Electron oscillations at ~ (1/2)₀ are preferentially excited inside a deep (|n/n_c|0.5) caviton although this is not deep enough to resonantly support (1/2)₀ oscillations. The experimental results show that the coupling between the (1/2)₀ electron oscillations inside the caviton and the electron plasma waves at (3/2)₀, which is originally excited due to the mode conversion of the incident microwave at the resonant layer and which generates the caviton, produces a localized nonlinear current which emits em waves at (3/2)₀. A similar coupling between (3/2)₀ and ₀ frequencies can emit em waves at (5/2)₀. The model to explain the above new phenomenon is discussed.Institute of Research and Development, and School of High Technology for Human Welfare, Tokai University, Japan. Department of Physics, University of California, Los Angeles, California. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 596–616, May, 1994.     

The temperature dependence of the conductivity and thermal emf due to multiphonon hopping in disordered semiconductors

Using transport theory, we studied the temperature dependence of the static conductivity and of the thermal emf due to multiphonon hopping in disordered semiconductors. In the low-temperature region when T < _m ( _m is the maximum phonon frequency), the temperature dependences of the conductivity and the thermal emf are the same as when single-phonon hopping is dominant. At higher temperatures (T _m), the hopping conductivity and thermal emf are characterized by a slower dependence on reciprocal temperature than in the low-temperature region.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.2, pp.42–47, February, 1976.The author is to V. L. Bonch-Bruevich and A. G. Mironov for discussing this work.     

Calculation of the Stokes-component amplification with bias illumination in the anti-Stokes region

The effect of Raman absorption in the anti-Stokes region on Stakes-component Raman scattering is discussed for the case of stimulated Raman scattering. It is shown that the Raman interaction leads to a significant amplification of the Stokes-component radiation and that the anti-Stokes radiation converts into Stokes radiation in proportion to the ratio _s/ _as.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 7, pp. 112–115, July, 1969.     

The proper formula for relative entropy and its asymptotics in quantum probability

Umegaki's relative entropyS(,)=TrD (logD –logD ) (of states and with density operatorsD andD , respectively) is shown to be an asymptotic exponent considered from the quantum hypothesis testing viewpoint. It is also proved that some other versions of the relative entropy give rise to the same asymptotics as Umegaki's one. As a byproduct, the inequality TrA logAB TrA(logA+logB) is obtained for positive definite matricesA andB.     

Theory of electric field-induced optical second harmonic generation in semiconductors

The nonlinear optical coefficientd _ij(kl) (2, 0,, ) for electric field-induced optical second harmonic generation in semiconductors is calculated by means of a perturbation treatment. The result is given directly as a Brillouin zone integral over a resonant energy denominator. A simplified energy band structure model is used to carry out the Brillouin zone integral. The analytic closed-form expression ford _ij(kl) (2, 0,, ) thus obtained permits the calculation of the absolute value of its spectrum from available energy band parameters. The dispersion ofd ₁₁₍₁₁₎ (2, 0,, ) of Ge is numerically calculated, second harmonic photon energies being close to theE ₀ andE ₁ gaps. The results show pronounced resonant behaviours.     

Separation of Variables for Bi-Hamiltonian Systems

We address the problem of the separation of variables for the Hamilton–Jacobi equation within the theoretical scheme of bi-Hamiltonian geometry. We use the properties of a special class of bi-Hamiltonian manifolds, called N manifolds, to give intrisic tests of separability (and Stäckel separability) for Hamiltonian systems. The separation variables are naturally associated with the geometrical structures of the N manifold itself. We apply these results to bi-Hamiltonian systems of the Gel'fand–Zakharevich type and we give explicit procedures to find the separated coordinates and the separation relations.