Conduction-electron Resonance Research Articles

Nonreciprocal Fabry-Perot effect and performance enhancement in a magneto-optical InSb-based Faraday terahertz isolator.

The Faraday effect due to the cyclotron resonance of conduction electrons in semiconductor InSb allows for nonreciprocity of transmitted light in our Faraday THz isolator operating in the presence of a small magnetic field. We select InSb as an efficient medium for our isolator due to its high electron mobility, low electron effective mass, and narrow band gap. Experimental measurements of the isolator performance indicate a maximum achieved isolation power of 18.8 dB with an insertion loss of -12.6 dB. Our optical analysis of the device points to a remarkable nonreciprocal Fabry-Perot effect in the magneto-optical InSb layer as the origin of the multi-fold isolation enhancement. This nonreciprocity occurs as the Fabry-Perot reflections in the forward direction add constructively and enhance the transmittance at certain frequencies, while the Fabry-Perot reflections in the backward direction add destructively and suppress the transmittance at the same frequencies.

Electron paramagnetic resonance study of the nuclear spin dynamics in an AlAs quantum well

The nuclear spin dynamics in an asymmetrically doped 16-nm AlAs quantum well grown along the [001] direction has been studied experimentally using the time decay of the Overhauser shift of paramagnetic resonance of conduction electrons. The nonzero spin polarization of nuclei causing the initial observed Overhauser shift is due the relaxation of the nonequilibrium spin polarization of electrons into the nuclear subsystem near electron paramagnetic resonance owing to the hyperfine interaction. The measured relaxation time of nuclear spins near the unity filling factor is (530 ± 30) min at the temperature T = 0.5 K. This value exceeds the characteristic spin relaxation times of nuclei in GaAs/AlGaAs heterostructures by more than an order of magnitude. This fact indicates the decrease in the strength of the hyperfine interaction in the AlAs quantum well in comparison with GaAs/AlGaAs heterostructures.

The Impurity Spin-Dependent Scattering Effects in the Transport and Spin Resonance of Conduction Electrons in Bismuth Doped Silicon

Transport and spin relaxation characteristics of the conduction electrons in silicon samples doped with bismuth in the 1.1·1013 - 7.7·1015 cm-3 concentration range were studied by the Hall and electron spin resonance spectroscopy. Hall effect measurements in the temperature range 10-80 K showed a deviation from the linear dependence of the Hall resistance in the magnetic field, which is a manifestation of the anomalous Hall effect. The magnetoresistance investigation shows that with current increasing magnetoresistance may change its sign from positive to negative, which is most clearly seen when the bismuth concentration goes up to 7.7·1015 cm-3. The conduction electron spin relaxation rate dramatically increases in silicon samples with sufficiently low concentration of bismuth ~ 2·1014 cm-3. All these results can be explained in terms of the concept of spin-dependent and spin flip scattering induced by heavy bismuth impurity centers.

Observation of conduction electron spin resonance in boron-doped diamond

We observe the electron spin resonance of conduction electrons in boron-doped (6400 ppm) superconducting diamond (${T}_{\text{c}}=3.8\phantom{\rule{0.28em}{0ex}}\text{K}$). We clearly identify the benchmarks of conduction electron spin resonance (CESR): the nearly temperature independent electron spin resonance signal intensity and its magnitude, which is in good agreement with that expected from the density of states through the Pauli spin susceptibility. The temperature dependent CESR linewidth weakly increases with increasing temperature, which can be understood in the framework of the Elliott-Yafet theory of spin relaxation. An anomalous and yet unexplained relation is observed between the $g$-factor, CESR linewidth, and the resistivity using the empirical Elliott-Yafet relation.

Conduction electron resonance used to determine size of palladium nanoparticles in proton conducting ceramics

A technique for determining the size of metallic nanoparticles incorporated into a ceramic is demonstrated using conduction electron paramagnetic resonance (CEPR). The resonances associated with palladium nanoparticles in a perovskite material are identified and studied as a function of temperature. As this line shape changes with temperature, the point at which the skin depth of the palladium is the same as the size of the nanoparticles is clearly identified due to a microwave saturation effect. This allows for a determination of their average size, which, in this case is 75±20nm. This is the first example of CEPR being used to determine metallic nanoparticle size in a technologically relevant, embedded in a non EPR-inert material system.

Identifying the electron spin resonance of conduction electrons in alkali doped SWCNTs

AbstractWe study the electron spin resonance (ESR) signal of pristine and potassium doped SWCNTs. We identify signals of a super‐paramagnetic background, a low intensity impurity, and of the conduction electron spin resonance (CESR). The latter only appears upon the alkali atom doping. To identify the CESR signal, we critically assess whether it could come from residual graphitic carbon, which we clearly exclude. We give accurate values for the signal intensities and the corresponding concentration of spins and for the g‐factors. The CESR signal intensity allows to determine the density of states on the SWCNT assembly.

EXCITATION OF CONDUCTION ELECTRON SPIN RESONANCE IN Si QUANTUM WELLS

The spin resonance of conduction electrons in a one-sided modulation doped quantum well in Si shows anomalies which we attribute to the microwave current induced Rashba field. We review results on the anisotropy of the lineshape, the amplitude and the temperature dependence which can be qualitatively explained in terms of this current-induced conduction electron spin resonance.

Electron spin resonance in Kondo systems

We calculate the dynamical spin response of Kondo impurity and Kondo lattice systems within a semiphenomenological Fermi liquid description, at low temperatures $T<T_K$, the Kondo temperature, and low magnetic fields $B \ll k_B T_K/g\mu_B$. Fermi liquid parameters are determined by comparison (i) with microscopic theory (numerical renormalization group) for the impurity model and (ii) with experiment for the lattice model. We find in the impurity case that the true impurity spin resonance has a width of the order of $T_K$ and disappears altogether if the $g$-factors of impurity spin and conduction electron spin are equal. However, there is an impurity-induced resonance contribution at the conduction electron resonance. The latter is broadened by spin lattice relaxation and is usually unobservable. In contrast, for the Anderson lattice in the Kondo regime we find a \textit{sharp} ESR resonance line only slightly shifted from the local resonance and broadened by spin lattice relaxation, the latter significantly reduced by both the effects of heavy fermion physics and ferromagnetic fluctuations. We conjecture that our findings explain the sharp ESR-lines recently observed in several heavy fermion compounds.

Tailoring Surface Plasmons through the Morphology and Assembly of Metal Nanoparticles

Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.

Effects of resonant polarons and band nonparabolicity on cyclotron resonance inn−InP

We study the effects of resonant polarons and band nonparabolicity on the cyclotron resonance of conduction electrons in $n\ensuremath{-}\mathrm{InP}$ at 4.2 K in the far-infrared regions. By combining photo- and electric field-excitation techniques, we successfully separate and estimate the individual contributions of resonant polarons and band nonparabolicity to the resonance magnetic field of the cyclotron resonance. In analyses of the experimental results obtained by use of the electric field excitation technique, we take into consideration the energy redistribution of conduction electrons by the electric field excitation. Those resonance magnetic fields are revised to the values for conduction electrons populating the bottoms of Landau levels, on the basis of the experimental results obtained by use of the photoexcitation technique. The dispersion of the resonance magnetic field is fitted by theoretical calculations using the improved Wigner-Brillouin perturbation theories by Lindemann et al. and the three-band $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ method by Lax. The conduction-band-edge mass ${m}_{e0}$ and the polaron coupling constant \ensuremath{\alpha} are used as fitting parameters. Excellent agreement between the experimental and theoretical results is obtained. We determine ${m}_{e0}{/m}_{\mathrm{fe}}=0.0788$ ${(m}_{\mathrm{fe}}$ is the free-electron mass) and $\ensuremath{\alpha}=0.12$ for InP.

Conduction Electron Resonance and Transport Properties of a Nonaligned Carbon Nanotube Thick Film for Field Emission Display

We present electron spin resonance spectra and the electronic transport characteristics of multiwalled carbon nanotubes (CNTs) which were screen printed in a thick‐film form for field emission displays. Electron spin resonance spectra showed a Dysonian line due to conduction electrons, and the reduced temperature dependence of the g‐value indicates the metallic properties of CNTs. Zero‐field resistivity and magnetoresistance were measured as a function of temperature T in the range 1.7–390 K and magnetic field, respectively. The resistivity of nanotubes for temperatures of 10–390 K indicates that the system is intrinsically metallic and the characteristics are well described by Mott's law in temperatures above 10 K. We found that the main contribution to the conductivity comes from carriers that hop directly between localized states via variable range hopping. The temperature dependence above 10 K is in good agreement with that of an individual multiwalled CNT. However, below 10 K, the resistivity is well fit to Efros' law, confirming the presence of a coulomb gap for the system. With a decrease of the temperature below 10 K the charge carriers in the system are localized by strong disorder, bringing a nearly insulating state. Using a diode configuration, we measured the field electron emission characteristics and found that the CNT thick film appears to emit electrons with a density of accompanying highly bright light emission. The emission current‐voltage characteristics can be fitted to a straight line in agreement with the Fowler‐Nordheim equation, which confirms that the emission current resulted from field emission of the CNT thick film. © 2000 The Electrochemical Society. All rights reserved.

Electronic properties of microcrystalline silicon investigated by electron spin resonance and transport measurements

The electron spin resonance and transport properties of microcrystalline silicon were investigated. Identification and location of the resonance states in the material are discussed. We analyse the properties of the conduction electron resonance and the relation of the corresponding states with electronic transport. Conduction band tail states within the crystalline regions of the material are proposed as a requirement for the interpretation of the experimental results.

Spin resonance of conduction electrons and EPR of localized moments in a low-dimensional organic conductor [Pd(dddt)2]Ag1.5Br3.5

The EPR spectra of a quasi-two-dimensional organic metal [Pd(dddt)2]Ag1.5Br3.5 contain signals due to the spin resonance of conduction electrons (CESR) and signals due to the localized magnetic moments of Ag2+. The system of Ag2+ ions exhibits a strong indirect antiferromagnetic exchange interaction characterized by the Weiss constant Θ=−280(25) K, which leads to magnetic ordering at a temperature of T0=70(10) K. The same temperature T0 corresponds to a strong anomaly in the CESR linewidth. The observed anomaly in the CESR linewidth, as well as some features of the temperature dependence of conductivity in the system studied, are explained by the interaction between conduction electrons and Ag2+ ions localized in the anion layers (π-d interaction) and by antiferromagnetic ordering of the spins of Ag2+ magnetic ions.

Determination of potential fluctuations in modulation-doped SiGe-quantum wells from conduction electron spin resonance

The spin resonance of conduction electrons in modulation-doped quantum wells is utilized to determine the density of states. The latter exhibits band tails resulting from potential fluctuations caused mainly by the distribution of charged impurities. Assuming a Gaussian distribution, we determine the fluctuation amplitude as a function of carrier density. For low-density screening becomes ineffective and we find a rapid increase of these fluctuations corresponding to the Anderson transition in two dimensions.

Electron magnetic resonance and optical properties of Ga 2−2 xIn 2 xO 3 solid solutions

Oxygen deficient Ga 2−2 x In 2 x O 3 (0≤ x≤0.5) solid solutions are investigated by means of optical absorption, fluorescence spectroscopies and electron spin resonance of conduction electrons. Optical spectroscopies show a decrease of the band gap when x increases. Electron spin resonance demonstrates that this phenomenon can be correlated to a progressive participation of indium orbitals in the conduction band edge. The predominant contribution of In-5s orbitals is responsible for a strong nuclear dynamic polarization, leading to the largest nuclear field B n=1.4 mT ever produced at high temperatures and low magnetic fields, for the composition with x=0.3. However, the expected bistability of the electron magnetic resonance resulting from this nuclear polarization is relatively small, most probably due to a disorder in the distribution of gallium and indium among the crystallographic sites. This disorder and the presence of Fe 3+ impurities is responsible for the variable magnetic properties of these compounds.

Doping and temperature dependence of paramagnetic states in microcrystalline silicon

Continuous wave and pulsed electron spin resonance (ESR) in the dark and under light illumination are used to study the doping and temperature dependence of defect, conduction electron and dopant states in microcrystalline silicon. Two resonances are found, which are attributed to silicon dangling bond states and located in different structural environments of the material. Light-induced ESR suggests that these two states have different energies, while in dark ESR, both show a wide and flat distribution in energy. The intensity of a third resonance from conduction electrons shows an almost 1:1 correlation with conductivity over three orders of magnitude. All resonances exhibit a Curie-like temperature dependence and the linewidth of the conduction electron resonance increases with temperature due to a decrease in the spin lattice relaxation time. Hyperfine interaction with phosphorus in n-type material and indications of hole states in p-type material are reported.

Stochastic resonance in an electron-spin–nuclear-spin system

We report a realization of stochastic resonance, based on the intrinsic bistability of the magnetic resonance of conduction electrons in gallium oxide [E. Aubay and D. Gourier, Phys. Rev. B 47, 15 023 (1993); D. Gerbault and D. Gourier, ibid 54, 6315 (1996)]. We show that the response to a small periodic magnetic field of the bistable conduction electron-spin-resonance signal can be amplified by the addition of an external random magnetic field. This is experimental evidence of stochastic resonance in the interaction of an electromagnetic field with an ensemble of two-level quantum systems (the Zeeman energy levels of free electrons).

Bistable magnetic resonance of conduction electrons in InP

The magnetic resonance of conduction electrons in InP exhibits a pronounced hysteresis with distorted line shapes. These features are quantitatively accounted for by considering the intrinsically bistable character of the dynamic nuclear polarization due to the Overhauser effect. The gross features of the resonance, its hysteresis, and the line shapes are controlled by the steady-state bistable nuclear field. It is shown that the effect of the long nuclear-relaxation time is compensated by the effects of the nuclear-field fluctuations. The respective contributions of the intrinsic bistability, the nuclear-relaxation rate, and the fluctuations are clearly identified by considering the bistable resonance as the overdamped motion of the spin system in a bistable potential.

Cyclotron resonance of conduction electrons in GaAs at very high magnetic fields

Cyclotron resonance of conduction electrons in GaAs at very high magnetic fields

Bistable Magnetic Resonance of Conduction Electrons in Solids

The phenomenon of bistable hysteresis in magnetic resonance of conduction electrons in solids is discussed, particularly the case of gallium oxide β-Ga2O3. This memory effect is a consequence of the dynamic polarization of nuclei by the Overhauser effect and manifests itself by a hysteresis of the ESR line provided that particular conditions for the external (or control) and internal (or material) parameters are satisfied. The influence of all these parameters on bistability is studied in detail. It is shown that magnetic resonance of conduction electrons in solids containing nonzero nuclear spins is an intrinsically bistable phenomenon. The reasons why bistability is so strong in gallium oxide even at room temperature, compared to other identified compounds where bistability exists only at very low temperature, are discussed in terms of electronic and crystallographic structure.