Conduction-electron Resonance Research Articles

Tunable bistable hysteresis of the magnetic resonance of conduction electrons in solids

Under dynamic nuclear polarisation by the Overhauser effect, conduction electrons in solids can exhibit a hysteresis of their magnetic resonance. In the case of polycrystalline samples of β-Ga2 O3 , a giant hysteresis can be achieved corresponding to a situation where the electron spins absorb the electromagnetic field when the magnetic field is swept downward and no absorption occurs in the reverse sweep direction. It is shown that this phenomenon is a general property of conducting solids containing elements with non-zero nuclear spins.

Magnetic Resonance of Conduction Electrons in Dislocated Germanium

AbstractPakulis and Jeffries first observed Zeeman transitions in germanium crystals which they attributed to the grown‐in dislocations. The authors explained the effect as a change of the electrical conductivity of the crystal due to spin dependent scattering of the carriers. The spin flip was ascribed to dislocation dangling bonds. Using plastically deformed germanium we can show that the signal is due to combined resonance of conduction electrons in one valley of the conduction band the energy of which is lowered by the strain field of dislocations. Additionally two more combined resonance lines are identified which also are assigned to the glide geometry. The delocalised states of electrons causing these lines by spin flip are not yet determined.

Bistability of the magnetic resonance of conduction electrons in gallium oxide

The EPR spectrum of {beta}-Ga{sub 2}O{sub 3} conduction electrons have different resonance fields in forward and backward magnetic field sweeps due to the dynamic polarization of Ga nuclei upon resonance saturation of conduction electron spins. This bistability results from a narrow line width and a strong isotropic hyperfine interaction that causes a large Overhauser shift. This phenomena is maximum at moderate electron spin system saturation. There is also evidence of a magnetic field memory. 25 refs., 9 figs.

Phonon-assisted electron resonance scattering effect in CeNi 5 point-contact spectra

It is shown that the conduction electron resonance scattering by Ce 4+- and Ce 3+-ions which occurs with the inelastic phonon scattering may result in additional phonon structure observed in the CeNi 5 point-contact spectra. Analysing the polarity influence on the point-contact spectrum, the 4ƒ-level scheme was determined.

Spin resonance of conduction electrons in carbon and nitrogen austenite

Comparative behaviour of the conduction electrons state density on the Fermi surface was studied by the conduction electrons spin resonance (ESR) method in the Cr20Ni16Mn6 steel type with carbon and nitrogen. It was shown that the state density increases with the nitrogen content below 1,6 at .% and decreases with carbon content. Preceding deformation also effects the spin resonance signal.

Magnetic resonance of conduction electrons in fluoranthene radical cation salts

The Overhauser shift method is a very sensitive technique to investigate the hyperfine interaction of conduction electrons with magnetic nuclei in organic conductors with a sufficiently narrow ESR line [1,2]. The high sensitivity is due to its double resonance character and is used to measure details of the proton NMR in single crystals. Despite an unresolved hyperfine structure, the average hyperfine tensor is accessible. Extension of the method uses magnetic nuclei like 13C, 19F and 2H in deuterated crystals as a local probe of the conduction electron spin density. Results for the (Fluoranthene) 2 .+PF 6 − radical cation salt are reported.

Electric-dipole spin resonance in n-type Cd1-xMnxSe.

A theoretical study of the electric-dipole-induced spin resonance of donor centers in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se is presented. The integrated absorption coefficient of far-infrared radiation in these materials is calculated considering the enhancement of the spin resonance caused by the admixture of orbital and spin states by the spin-orbit coupling. In semiconductors with the wurtzite structure (e.g., CdSe), the spin-orbit interaction is of the parity-nonconserving form (\ensuremath{\lambda}/2\ensuremath{\Elzxh})c^\ensuremath{\cdot}(\ensuremath{\sigma}\ifmmode\times\else\texttimes\fi{}p) where c^ is a unit vector along the ${C}_{6}$ axis, \ensuremath{\sigma} and p the Pauli spin and momentum operators, and \ensuremath{\lambda} a constant characteristic of the material. We calculate the integrated intensity and compare the results with the experimental finding of Dobrowolska et al. A fit of the theoretical curves to the data yields \ensuremath{\lambda}=6.4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ eV?. We also present a discussion of the electric-dipole-enhanced spin resonance of conduction electrons in semiconductors with the wurzite structure.

Electric-dipole and magnetic-dipole interference in the spin resonance of conduction electrons in Wurtzite semiconductors

Recent studies of magnetotransmission in n-type InSb revealed an unusually strong conduction electron spin resonance which changed upon reversal of either the applied magnetic field B → o or the direction of propagation q → of the incident radiation. This was attributed to an interference between electric-dipole and magnetic dipole interactions, the former being allowed by a spin-orbit interaction lacking inversion symmetry. We study here a similar phenomenon for conduction band electrons in semiconductors having the Wurtzite structure.

Dynamical Behaviour of Photoexcited Electron System in Gallium Arsenide

In this work we report on the first observation of the far-infrared Baser (119–220 µm) magneto-optical absorption by the photoexcited electron system in GaAs up to the magnetic field of 50 kG over the temperature range of 1.7–4.2 K. The major absorption lines observed for various samples are the 1s→2p +1 . Zeeman transition and the cyclotron resonance of conduction electrons. It is found that both absorption line-widths are sensitive to impurity concentration and to conduction electron density. The magnitude of the electron-electron scattering and that of the electron-neutral impurity scattering under the quantum limit condition are thereby discussed.

Enhanced Raman spectroscopy of CO adsorbed on vapor-deposited silver

Raman spectra of CO condensed on vapor-deposited Ag at 11 K show two signals in the CO stretching region, one originating from a monolayer next to the metal, the other from the bulk CO film above it. In addition, a low-frequency band associated with the former was detected, as were overtones of both the low- and high-frequency bands of the surface CO. Raman scattering by the former was found to be some 106 times more intense than by the latter on a per molecule basis. The state of polarization of the tow signals was investigated as a function of angle of incidence, as was the excitation profile of the signal from the CO next to the metal, using the bulk CO signal as a reference. The behavior of the latter could only be understood when one took into account coherence effects arising from the superposition of rays directly incident on or scattered by a molecule with those reflected from the metal before impinging on, or after scattering from, the molecule. These effects could give rise to apparent polarizing or depolarizing effects and warrant attention in matrix isolation Raman spectroscopy as well as in surface Raman spectroscopy. Taking all observations into account, the enhanced Raman is suggested to be a form of resonance Raman by CO-covered, metal surface irregularities which act as ’’adsorbed,’’ giant cluster compounds, the metal core of which is large enough to sustain conduction electrons, thereby allowing the conduction electron resonance to become an electronic state of the pseudoadsorbed cluster. It is this electronic state which is in resonance with the incident illumination. The relationship between this electronic resonance and surface plasma resonance in an isolated metal sphere is pointed out. The expected enhancement of molecules adsorbed on several metals other than silver is estimated in the context of the model proposed. Group IB metals are shown to be premier among the enhancers, although Cu and Au should be most efficatious in the red.

Cyclotron resonance study of conduction electrons in n-type indium antimonide under a strong magnetic field. (I) thermal equilibrium case

Abstract The far IR cyclotron resonance of conduction electrons is investigated in n-type indium antimonide in the quantum regimes, ħω c k B T and ħω c ⪢ k B T . The resonance peak position, half width, and the degree asymmetry in the line shape are studied as a function of temperature. In analyzing the experimental data, the three band model has been employed together with modern theoretical results of electron scattering by ionized impurities in the presence of a strong magnetic field. It is found that, for example for an experiment at 84 μm, the Une width depends very little on temperature between 4.2 and 45 K where the ionized impurity scattering is dominant, and increases rapidly with temperature above 45 K where the onset of phonon scattering is expected. Further details of the ionized impurity scattering were investigated by using three different laser wavelengths 84, 119 and 172μm. The line width at the phonon-limited temperature region depends very little on magnetic field and sample. The temperature dependence of the band gap was also determined by analysis of the resonance peak shift.

Study of spin resonance in Hg1− xCdxTe by four-photon mixing

Four-photon mixing is used to measure spin resonance of conduction electrons in Hg 1− x Cd x Te ( x = 0.23). The magnetic tuning rate and the motionally narrowed linewidth are studied experimentally below and through the quantum limit and comparison is made with theory.

Cyclotron resonance study of conduction electrons in n-type indium antimonide under a strong magnetic field—I: Thermal equilibrium case

The far IR cyclotron resonance of conduction electrons is investigated in n-type indium antimonide in the quantum regimes, ħω ck BT and ħω c ⪢ k BT . The resonance peak position, half width, and the degree asymmetry in the line shape are studied as a function of temperature. In analyzing the experimental data, the three band model has been employed together with modern theoretical results of electron scattering by ionized impurities in the presence of a strong magnetic field. It is found that, for example for an experiment at 84 μm, the Une width depends very little on temperature between 4.2 and 45 K where the ionized impurity scattering is dominant, and increases rapidly with temperature above 45 K where the onset of phonon scattering is expected. Further details of the ionized impurity scattering were investigated by using three different laser wavelengths 84, 119 and 172μm. The line width at the phonon-limited temperature region depends very little on magnetic field and sample. The temperature dependence of the band gap was also determined by analysis of the resonance peak shift.

Sample size effects on the spin resonance of conduction electrons in silver

The CESR linewidths of evaporated films of silver, deposited on quartz substrates, have been measured at 9.27 GHz. An increase in low temperature linewidth with decrease in thickness over the range 1.1 μm to 0.5 μm is observed. Below 13 K, ϵ, the probability of an electron losing its spin memory on colliding with the surface, is found to be about 4.10-4.

Coupled electron spin resonance of non-S-state impurities in metals

The dynamical coupling of the individual crystal-field transitions and the conduction electrons is investigated for non$S$-state ions in an arbitrary crystal field. The equations given are the result of a microscopic quantum-statistical treatment. All relevant terms of the transition matrix have been calculated in the lowest nonvanishing order of perturbation theory. The results allow a quantitative description of the experimental ESR spectra. A particular physically realistic example is discussed in detail. A large temperature-dependent $g$ shift and a decrease of the width with increasing concentration is found for the local-moment resonance. At high temperatures the coupling to the excited states plays an important role and in particular affects the conduction-electron resonance shift. The relevance of these effects for actual physical situations is discussed in some detail.

Temperature dependence of dynamic conductivity of electrons in the surface inversion layer of semiconducting silicon

The cyclotron resonance of conduction electrons in a semiconducting silicon (100) surface inversion layer is studied by using the memory-function approach. The effects due to electron-impurity and electron-electron interactions are included. The cyclotron-resonance mass shift and the transport lifetime are calculated as functions of temperature, electron concentration, and frequency in the absence of a magnetic field. The obtained mass shift as a function of temperature is compared with the measurement of Kennedy et al., and the agreement is only qualitative.

Lineshapes of the electron paramagnetic resonance of small silver particles

The lineshape of the electron paramagnetic resonance of conduction electrons of small silver particles is analyzed in terms of the theory of Kawabata and the size distribution of the particles in the sample. In particular, this analysis explains the observed asymmetry of the signal and its evolution during the heat treatment of the samples.

Sample Size Effects on the Spin Resonance of Conduction Electrons in Aluminium

AbstractThe CESR residual line widths of cold rolled aluminium foils and evaporated aluminium films have been measured at 9.27 GHz for samples of thickness 0.1 to 38 μn. An increase in line width with decrease in thickness is observed at low temperatures. This increase is attributed to spin scattering of the conduction electrons at the aluminium surface. Below 20 K, ϵ, the probability for an electron losing its spin memory on colliding with the surface, is found to be less than 2.3 × 10−3 for foils and lies within the range 1.0 × 10−4 to 1.9 × 10−3 for films.

Polaron cyclotron resonance in AgBr at microwave and infrared frequencies

The cyclotron resonance of conduction electrons in AgBr has been measured at 136 GHz and at 891 GHz. The apparent effective 'mass' of the electrons is greater by 5.2 per cent at the higher frequency. This increase is compared with the predictions of polaron theory. Good agreement exists with a variational calculation by Larson which assumes the interaction Hamiltonian of Frohlich and a wavefunction based on a modified one-phonon Tamm-Dancoff approximation.

Linewidth of acoustic spin resonance of conduction electrons

The acoustic spin resonance linewidth is calculated and its connection with the operator structure of the spin-sound interaction Hamiltonian is shown. The ultrasonic frequency regions where the resonance can be observed are found.