59Co nuclear magnetic resonance in antiferromagnetic CsCoCl3

The ⁵⁹Co NMR in a CsCoCl₃ single crystal has been observed by the spin echo method at 4.2 K. The obtained spectrum is composed of seven distinct lines split by the nuclear-quadrupole interaction. The frequency of the central (± $\text{1}\text{2}$ ? ± $\text{1}\text{2}$) transition 502.08±0.05 MHz corresponds to the hyperfine field of 499.38 ± 0.05 kOe, which agrees well with the calculated value. Due to the interaction of the nucleus with the electronic moment induced by the external field, a shift as large as 18% was observed for the nuclear g-factor.     

Magnetic field dependence of the nuclear spin—lattice relaxation of 93mMo and 94,95Tc in Fe

The nuclear spin—lattice relaxations of ^93mMo$\text{Fe}$ and ^{94, 95}Tc$\text{Fe}$ at T ? 10 mK have been investigated with frequency- modulation-pulsedNMR on oriented nuclei as a function of an external magnetic field B₀. In the range 0?B₀?6kG the relaxation constant varies by a factor >10 and ?6 for ^93mMo$\text{Fe}$ and ^94,95Tc$\text{Fe}$, respectively. The high-field Korringa constants for ^93mMo, ⁹⁴Tc and ⁹⁵Tc in Fe were determined to be 2.5(4), 1.3(4) and 0.55(10) sK.     

Z(2) vortices and the SU(2) string tension

Topologically determined Z(2) variables in pure SU(2) lattice gauge theory are discussed. They count the number of “vortex souls”. The high temperature expansion for the corresponding Z(2) loops is examined. They obey an area law. The coefficient of the area is shown to be equal to the string tension to all orders of the high temperature expansion. This shows that the string tension is determined by the probability distribution of the vortex souls, at least in the high temperature region. The dependence of the string tension α(β, h) on an external field h that is coupled to the Z(2) field strength is calculated to lowest order of the high temperature expansion. In this approximation, α(β, h) is determined by the free energy of a 2-dimensional Ising model in an external magnetic field $\text{1}\text{2}\text{log}\text{(β/4}\text{tanh}\text{h)}$ at an inverse temperature $\text{1}\text{2}\text{log}\text{3}\text{4}\text{π = 0.429}$.     

Optical line narrowing by nuclear spin decoupling in Pr3+: LaF3

We have applied the technique of nuclear spin decoupling to the optical regime. In these experiments we selectively eliminated the role of ¹⁹F spin fluctuations as the dominant source of dephasing in the 5925A (¹D₂ / ³H₄)Pr³⁺ optical transition in 0.05% Pr³⁺: LaF₃ at 2K. The homogeneous optical linewidth (FWHM), measured by photon echoes, was reduced from 56 kHz to 6 kHz by on-resonance nutation of ¹⁹F in an external magnetic field of 375G. Further reduction of the linewidth to 4.1 kHz was observed by off-resonance irradiation of the fluorines such that their effective field in the rotating frame was at the ‘magic angle’ ($\text{cos}{}^{-1}\text{1}\text{3}$) with respect to the external field.     

A generalization of the fluctuation-dissipation theorem for the case of excess noise

Electrical fluctuations proportional to the square of the external field are investigated in the case of quasiequilibrium conditions. The binary correlation fluctuation proportional to the square of the external field is expressed in terms of the zero-field quaternary correlation function for both quantum and classical cases. This result can be considered as a generalization of the fluctuation-dissipation theorem. As applied to the electrical $\text{1}\text{f}$ noise the novel method investigation both in theory and in experiment is presented. The frequency dependence of zero-field quaternary potential correlation function is suggested to be investigated instead of binary correlation function proportional to the square of external field.     

On the field penetration into semiconductors in the field ion microscope

The calculation of field penetration in semiconductors and consequent band bending during field ionization/evaporation is discussed. The shielding by surface states is also taken into account. The Si(111) face example demonstrates that neglection of surface states may give unrealistic high band bending values. Because of the lack of reliable data for the density of surface states, a possible maximal band bending has been calculated for GaAs. Its value in the case of an external applied field of $\text{1}\text{V}\text{A}\text{?}$ may be such smaller as formerly assumed in recent works.     

Intersections of quasi-energy levels in the relativistic theory of multiply charged ions

The relativistic generalization of the quasi-energy method is given with the help of which the influence of an alternating electric field on the energy levels (2 $\text{1}\text{2}$ 0), (2 $\text{1}\text{2}$ 1) of multiply charged H-like ions is investigated. Intersections are found of quasi-energy levels in external fields with frequencies ω₀ ? ΔE_L and definite values of the field amplitude.     

Nuclear orientation of 109Cd and 115mCd in Cd

The quadrupole interaction frequencies of ¹⁰⁹Cd$\text{Cd}$ and ^115mCd$\text{Cd}$ have been measured by low-temperature nuclear orientation as +110(4) MHz and -102(12) MHz, respectively. The electric field gradient of Cd$\text{Cd}$ and the quadrupole moment of the $\text{5}\text{2}$⁺ 245 keV level of ¹¹¹Cd are deduced.     

Subthreshold K− production by coherently produced π-mesons in heavy ion collisions

We assume that the enhanced subthreshold K^? production found recently in the reaction ²⁸Si? ²⁸Si at 2.1 $\text{GeV}\text{nucleon}$ is due to the decay of coherently produced π-mesons. We calculate the differential K^? production cross section by treating the source term of the π-meson field, which is the nucleon current, as an external c-number source. We parametrize this current by assuming a diving, a compression, and an expansion stage during the nucleus-nucleus collision where the results of the intranuclear cascade calculations serve as a reference. Assuming a reasonable time for building up three times the normal nuclear matter density we get agreement with the experimental data. We predict a differential cross section that is different from a thermal spectrum.     

Superradiation from non-ideal plasmas in electric field

An effect of external static electric field on emission of radiation from non-ideal plasmas of erosion focus has been experimentally observed. An order-of-magnitude increase in radiation intensity for spectral interval hv = 40 ? 350 eV with electric field increasing up to 10³V/cm has been found for plasmas with $\text{ξ}\text{Z}\text{?1}$, where ξ is the number of electrons in Debye sphere, Z = 2 ? 3 is the stage of ionization. The energy emitted has been several times higher than the black body energy for the same spectral interval at maximum electric field achieved. The effect vanishes at $\text{ξ}\text{Z}\text{?10}$.     

Dirac dynamics on stochastic phase spaces for spin 1/2 particles

The Foldy-Wouthuysen representation of the dynamics of a free spin $\text{1}\text{2}$ particle is formulated in a Hilbert space $\text{H}$(Γ) of spinor-valued functions over Γ-space. $\text{H}$(Γ) carries a reducible Wigner-type representation of the Poincaré group. The transition to the Dirac representation in a new bispinor Hilbert space $\text{K}$(Γ) is effected by means of a generalized inverse Foldy-Wouthuysen transformation. Explicit expressions are derived for the resolution generators η of invariant subspaces $\text{K}$±(Γ_η) carrying irreducible representations of the resulting representations of the Poincaré group. The formalism is recast in a manifestly covariant form and the Dirac equation on $\text{H}$(Γ_s) with minimal coupling to a four-potential is examined. It is shown that the resulting external field theory is gauge-invariant and relativistically covariant.     

Differential susceptibility of spin glass - ferromagnetic systems

The differential susceptibility of double transition spin glass - ferromagnets is calculated as a function of temperature and external field based upon the theory by Sherrington and Kirkpatrick. Good agreement with experiments on the $\text{Pd}$FeMn system has been obtained.     

Variation of the local field through the liquid-vapour interface

We derive an integral equation for the self-consistent local field E^loc(z) within an inhomogeneous non-polar fluid, with particular application to the liquid-vapour interface. Approximate solutions are given for the cases of induced atomic dipoles oriented perpendicular and parallel to the interface. For the perpendicular case we relate the average field to the local field and thus obtain an equation for the static dielectric constant ?(z) in terms of the density profile n(z). The departures of the local field from Lorentz form $\text{E}{}^{\mathrm{<mtext>ext</mtext>}}\text{/(1 + (}\text{8}\text{3}\text{)παn(z))}$ and of the dielectric constant from the Clausius-Mossotti form ($\text{1 + (}\text{8}\text{3}\text{)πan(z))/(1 ? (}\text{4}\text{3}\text{)παn(z))}$ are shown to be small. For the parallel case we discuss fringing of the external field and show that the dipoles align themselves with the average field, not the external field. The departure of the local field from $\text{E}{}^{\mathrm{<mtext>ave</mtext>}}\text{/(1 ? (}\text{4}\text{3}\text{παn(z))}$ is shown to be small.     

Change in the order of a martensitic phase transformation by an external field

It is shown on the basis of the Labbé-Friedel model for A₃B compounds that the martensitic phase transformation in Nb₃Sn can be changed from a first to a second order transition by an external stress. The Hamiltonian operator describing the phase transition in an external stress field has been mapped to a spin $\text{1}\text{2}$ Ising model with infinite range interactions showing a second order phase transition. Estimates of the transition temperature and the maximum order parameter are given suggesting new experiments.     

Nuclear magnetic resonance of extremely dilute CrFe

We report nuclear orientation and pulsed NMR on radioactive ⁵¹Cr$\text{Fe}$ samples. The zero-field resonance frequency of 13.543(18) MHz from polycrystalline foil samples yields a hyperfine field B_hf = ?6.655(35) T in the dilute, low-temperature limit for Cr$\text{Fe}$.     

Evidence for the helical spin structure due to antisymmetric exchange interaction in Cr13NbS2

It is pointed out that the helical spin structure due to antisymmetric exchange interaction can be distinguished from the one of usual origin by observing its behavior under the external magnetic field. This type of helical structure is shown to be realized in Cr_{$\text{1}\text{3}$}NbS₂ from analyses of magnetic and neutron diffraction measurements.     

Nonlinear response to external magnetic fields

The purpose of this paper is to study conditions under which a system of itinerate spin-$\text{1}\text{2}$ fermions might exhibit a macroscopic linear response to external magnetic fields after long times. Exact expressions are obtained for the nonlinear response of the magnetization and the total energy. We find that for a constant field there is no response (our model contains no mechanism for the relaxation of spins). For an oscillatory field there is a response in which secular terms (in the time) appear which are associated both with nonlinear terms in the external field and with contributions from the background medium. The secular terms involving the magnetic field would not be seen if one used the usual approximations of microscopic linear response theory. They give rise to new conditions which must be satisfied if the system is to exhibit a macroscopic linear response in the long-time limit.     

Spectral density approach for the damping of fermion elementary excitations in an anisotropic spin-12 linear chain

The paper is devoted to an investigation of the damping effects of the Fermion elementary excitations in the Jordan-Wigner representation of a one-dimensional anisotropic $\text{spin-}\text{1}\text{2}$ model in an external field. This is realized on the basis of the “Gaussian ansatz”, recently proposed by Nolting and Oles, as substituting the standard “polar ansatz” in the Spectral Density Method, for exploring damping effects of quasi-particles in many-body problems. By using a first order approximation, we are able to obtain reasonable results in the low temperature limit.     

The effect of external electric fields on molecular liquids and induced translational motion

A computer simulation is reported of the enantiomer S CHBrClF subjected in the liquid state to intense external fields of force : i) uniaxial electric field E_Z; ii) circularly polarised field at optical frequencies. The molecular dynamics are quantified in detail at field - on equilibrium in case i) using a range of auto correlation functions. The foremost result of the investigation is that the simple uniaxial field E_Z makes the sample $\text{translate}$ in a well defined direction. The direct effect of E_Z on an isolated molecule of S-CHBrClF is purely rotational, but intramolecular rotation/translation coupling converts this rotation into coherent centre of mass translation. This gives rise to direct, $\text{laboratory frame}$, cross correlations of the type <v(t)$\text{J}$^T(o)> where $\text{v}$ is the molecular centre of mass translational velocity and $\text{J}$^T the transposed molecular angular momentum vector. (The existence of these invalidates the classical theory of the Kerr effect.) The molecular dynamics of the hypothetical chiral ion S-CHBrClF^? are looked at with a view to corroborating the predictions by Baranova et al. concerning their response to electric field treatment. Despite the inherent instability of such an ensemble of like-charged ions the simulation can be used to produce a range of auto and cross-correlation functions with which to characterise the ionic dynamics. The effect of treating the ionic ensemble with a field E_Z is reported briefly in terms of the non-vanishing ensemble averaged centre of mass velocity <v_Z&>;.The induced translation in an electric field may be demonstrated on most liquids using a simple experimental set up. Its importance in optically active systems is such that it may be used to separate a racemic mixture into its enantiomers, the translational motion induced in the one enantiomer is necessarily, by symmetry, opposite to that induced in the other enantiomer. The observation therefore has technological importance. Other applications are discussed.