Effect of positive muon trapping by dislocations

Aluminum was deformed at room temperature so that vacancies are annealed out and only dislocations are remained. The muon spin depolarization rate was found to be decreased as the temperature is raised. This indicates that some trapping-detrapping occur. Fitting the spin relaxation to the calculated spin relaxation function for the trapping-detrapping model, the values of the activation energy for the trapping rate and detrapping rate and of the depolarization rate at the trapping are found to be 25 meV, 66 meV, and 0.24 sec^–1, respectively for the best fit. This indicates that positive muons diffuse to dislocations and diffuse along dislocation lines and are trapped at a jog of the dislocation, and detrap from the jog.     

Diffusion,trapping and detrapping of positive muon in Al-0.047% Mg

Positive muon spin relaxation was measured in Al-0.047% Mg quenched from 873 K under zero external magnetic field from 6.3 K to 270 K. The observed spectra were analysed with the calculated muon spin relaxation function which included the static relaxation rates, the trapping rates, the detrapping rates and thet=0 initial trapping fractions. Due to the precise measurements and the realistic expression of spin relaxation function, above four parameters could be determined distinctly. The trapping rates and the distortions around a muon were determined from the values of static relaxation rates at a trapping site. The diffusion features were clearly described by the trapping and detrapping rates. The diffusion process was determined by the temperature dependence of these parameters.     

Zero-field muon spin relaxation reflecting dynamics of spin glass

The muon spin relaxation function is calculated in a fluctuating random dilute spin system, and the effect of Edwards—Anderson's order parameter is considered in a time-dependent treatment. The results demonstrate the unique capability of zero-field μSR probing spin glasses.     

Electron–muon dynamics in n‐type silicon

We report RF‐μSR results in lightly n‐doped Si samples. Measurement of the diamagnetic amplitude in both the \langle 100\rangle and \langle 111\rangle directions for a sample with N_D\leq5\times 10¹²\ cm^-3 clarifies the charge/spin electron‐exchange dynamics for bond‐centered muonium and yields a 3300 Å ² electron‐capture cross section at Mu⁺ _BC. An increase in the Mu⁰ _BC RF amplitude observed at 30K in a sample of N_D\simeq 2\times 10¹³\ cm^-3 provides direct evidence for enhanced low‐temperature creation of Mu_BC ⁰ at the expense of Mu_T ⁰0 with increased electron concentration.     

Spin dynamics of the muon in muonium in normal metals

The question of the charge state of the proton (the positive muon) in metals is of fundamental importance for the theory of metal hydrides. The theory developed here permits determination of the charge state of μ ⁺ in normal metals. The experimental possibilities of the observation of Mu atoms in metals at various strengths of the external magnetic field and various temperatures are analyzed. Zh. éksp. Teor. Fiz. 111, 730–736 (February 1997)     

Kinetics of muon catalyzed fusion processes in solid H/D mixture

This paper presents the final results of an experimental study of the kinetics of the muon catalysed fusion (MCF) in solid hydrogen-deuterium mixtures (H/D) at a temperature of 3 K. The experiment E742 was carried out on a TRIUMF meson facility in Canada. Four exposures were performed at different deuterium concentrations in the H/D mixture: c_d = 0.0005, 0.02, 0.15 and 0.75. A simultaneous analysis of the measured time distributions of the 5.5 MeV γ-quanta and the 5.3 MeV conversion muons obtained from nuclear fusion in the pdμ molecule allowed to extract the values of MCF chain parameters in the H/D mixture: the fusion partial rates for different nuclear spin states of the pdμ molecule, and the pdμ molecule formation rate. The experimental data fitting procedure was conducted in two ways: using solely the analytical formulae describing the kinetics of the MCF processes in the H/D mixture, and the detailed Monte Carlo simulation of the entire experiment. The results obtained by these two methods are consistent with each other and confirm the existence of the Wolfenstein-Gerstein effect.     

Quantum and stochastic aspects of low-temperature trapping and reaction dynamics

We discuss theoretical work on motion-limited trapping kinetics at very low temperatures where theories based upon strictly diffusive models break down due to quantum mechanical effects. In addition, we present numerical results which confirm earlier asymptotic predictions regarding the survival probability for one-dimensional chains, and discuss the important role fluctuations and selfaveraging (or the lack thereof) play in the analysis of finite systems.     

Spin dynamics in CuGeO3 studied by muon spin rotation

We report a muon spin rotation (SR) study of the magnetic properties of the Cu²⁺ quasi-one-dimensional CuGeO₃ system and its lightly-doped derivative Cu_0.97Zn_0.03GeO₃. Susceptibility measurements on CuGeO₃ show a sudden change in the vicinity of 14 K that has been interpreted before as a magnetic transition to a spin-Peierls state. SR shows no evidence of spin freezing below 14 K, implying that the transition is to a magnetic state with no static (random or ordered) electronic moments. A modest slowing down of the electronic spin dynamics is also identified at this temperature. Similarly, no evidence of a transition to a static magnetic state is found for Cu_0.97Zn_0.03GeO₃ whose susceptibility shows hysteretic behaviour between zero-field and field cooled measurements at 4 K, previously ascribed to spinglass-like behaviour. Given the nature of the muon spin as a local magnetic probe, the present results necessitate a re-interpretation of the origin of the susceptibility anomaly observed in the doped system.     

Spin dynamics in magnetic materials investigated by muon spin relaxation

We present a quantitative analysis of the temperature dependence of the muon spin relaxation rate measured in simple magnets. We consider the low temperature, critical and high temperature regimes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spin-glass dynamics determined from muon spin relaxation and neutron spin echo measurements

Muon spin relaxation (SR) and neutron spin echo (NSE) measurements of magnetic ion correlation times and correlation functions in the spin glass systemsCuMn,AgMn, andAuFe are compared. It is found that theSR and NSE measurements are in excellent agreement both above and below the spin-glass freezing temperatures. The experimental results are compared to recent theories of spin-glass dynamics.We are grateful to D.L. Huber and R.E. Walstedt for stimulating discussions. This work was performed under the auspices of the U.S. Department of Energy, and was also supported by the U.S. National Science Foundation, Grant No. DMR-8115543.     

Spin dynamics of geometrically frustrated spin systems observed by muon spin relaxation

μSR is shown to be a sensitive probe of fluctuating internal magnetic fields in geometrically frustrated magnets. The usefulness of μSR in these systems is illustrated in the case of pyrochlores, in which the antiferromagnetically coupled ions occupy a lattice of corner sharing tetrahedra. Remarkably, one observes a type of spin freezing in Y₂Mo₂O₇ and Tb₂Mo₂O₇ which is similar to that seen in conventional spin glasses, even though there is no detectable structural disorder. Unlike ordinary spin glasses these geometrically frustrated antiferromagnets display unusual low temperature spin dynamics which persist down to the lowest accessible temperatures.     

Propagation dynamics and optical trapping of a radial Airy array beam

Analytical propagation expression of a radial Airy array beam in coherent and incoherent combination passing through paraxial ABCD system is derived, and used to investigate the effect of combination scheme, array orientation and initial phase of Airy beamlet on propagation dynamics of the resulting beam in free space, where optical spot array and vortex array with different shapes are also found, respectively. And then taking four-beamlet Airy array beam in same array orientation as an example, square optical spot array obtained in focal field can be used for simultaneous trapping multiple Rayleigh particles with relative refractive index larger than 1. The transverse gradient forces serving as restore forces tend to push particles at different initial positions to their individual optical spot center. The analysis of trapping stability indicates that larger input peak intensity of Airy beamlet and smaller particle size are benefit to trapping particle owing to many deeper potential wells. Vortex array produced by coherent combined Airy array beam in this paper is expected to be useful for simultaneous trapping microparticles with relative refractive index smaller than 1.     

Optical nonlinearities and carrier trapping dynamics in CdS and CuxS nanocrystals

Application of femtosecond photoluminescence and nonlinear transmission techniques allows us to separate electron and hole relaxation paths in CdS nanocrystals (NCs) and to observe a strong difference in optical nonlinearities in NCs formed by direct- and indirect-gap phases of copper sulfide.     

Kinetics of Brownian particle trapping by randomly distributed traps of various sizes

Diffusion of a particle in a medium in the presence of absorbing traps of various size is considered. A theory describing the kinetics of particle trapping in the entire interval of time is suggested. Analytical relations for the probability of a particle survival in situations when many-body effects are weak and when they dominate are obtained. It is shown that polydispersity of traps leads to the slowdown of particle trapping and to attenuation of many-body effects inherent in the problem.     

First principles electronic structure investigation of order of singlet and triplet states of oxyhemoglobin and analysis of possible influence of muon trapping

Interest in the possibility of magnetic character for oxyhemoglobin (OxyHb) has been recently stimulated by the observations of muon spin-lattice relaxation effects studied (Nagamine et al., Proc Jpn Acad Ser B Phys Biol Sci 83:120–126, 2007) with the muon-spin rotation (μSR) technique. In view of this, we have carried out first-principles electronic structure investigations involving Hartree–Fock theory combined with many body perturbation effects for the singlet and triplet states of OxyHb. Our results indicate that using two recent x-ray structural data (Paoli et al., J Mol Biol 256:775, 1996; Park et al., J Mol Biol 360:690, 2006) for OxyHb, for only Hartree–Fock theory without many-body effects included, the singlet state lies above the triplet state by energies of about 0.08 and 0.13 a.u. for the two structures in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). Incorporation of many-body effects by the perturbation method reverses the order, with the triplet state located 0.18 and 0.14 a.u. above the singlet state for the structures in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). Physical reasons for these relative orderings of the singlet and triplet states will be discussed. It is clear that OxyHb by itself would be in a singlet state at room temperature or below, since from our calculation, the triplet state lies about KT above the singlet state with T having the value of 44,098 K and 56,449 K for the two structural data in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). As regards the muon spin-lattice relaxation effects obtained by recent μSR measurements (by Nagamine et al., Proc Jpn Acad Ser B Phys Biol Sci 83:120–126, 2007) at room temperature, the sensitive dependence of the singlet-triplet separation on many-body effects in our investigation suggests that it is possible that the singlet-triplet separation could be reversed or reduced significantly when a muon is trapped near an oxygen atom of the oxygen molecule, allowing the triplet to be occupied at room temperature and lead to significant muon spin-lattice relaxation.     

Spin dynamics in Cd1−xMnx Te studied by muon spin rotation

Spin fluctuations in Cd_1−xMn_xTe (x=0.05, 0.10, 0.20, 0.30, 0.40, 0.54, 0.60, 0.68) were studied by the muon spin rotation (μSR) technique. Correlation times of the Mn-spins are deduced from the muon depolarization rates. A strong increase of the depolarization rate near the Mn-spin freezing temperature is observed. At 88 K, larger depolization rates are found forx=0.10 andx=0.20 than for higher Mn-concentrations, indicating that the exchange narrowing is considerably reduced (spin fluctuations slow down) for lower Mn-concentrations.     

Unparticles and muon decay

Recently Georgi has discussed the possible existence of ‘Unparticles’ describable by operators having non-integral scaling dimensions. With the interaction of these with the Standard Model particles being constrained only by gauge and Lorentz symmetries, it affords a new source for lepton flavour violation. Current and future muon decay experiments are shown to be very sensitive to such scenarios.     

Coverage dependence of neopentane trapping dynamics on Pt(111)

Adsorption probabilities for neopentane on Pt(111) were measured directly using supersonic molecular-beam techniques at coverages ranging from zero to monolayer saturation, incident translational energies between 18 and 110 kJ mol⁻¹ and incident angles between 0° and 60° at a surface temperature of 105 K. The adsorption probability was found to increase with coverage up to near monolayer saturation at all incident translational energies and incident angles. The coverage dependence of the adsorption probability predicted by a modified Kisliuk model with enhanced trapping into the second layer exhibits good quantitative agreement with the experimental values. The angular dependence of the adsorption probability decreases with increasing coverage, suggesting that the effective corrugation of the gas–surface interaction potential increases with the adsorbate coverage. The initial adsorption probability into the second layer onto the covered surface decreases from 0.95 to 0.75 with increasing energy over the energy range studied, and exhibits total energy scaling. A comparison with second-layer trapping data of simpler molecules onto covered Pt(111) indicates that the structural complexity of adsorbed neopentane molecules facilitates collisional energy transfer during adsorption.     

Contribution of prompt muon production to total muon fluxes

Summary The flux of prompt cosmic-ray muons coming from charmed particles which are produced in both nondiffractive and diffractive processes of primary-air collisions is computed. Its maximum contribution is estimated by stressing the diffractive character of produced charmed particles. We compare the observed results on angular distributions of muon intensities at a given depth with the calculated results. There is no clear evidence for prompt muons. In a more quantitative analysis, χ² tests with regard to the expected form of the muon spectrum are performed. The expectation is based on a formula of Thompson and Walley for muons coming from pion and kaon decay which shows a sec θ enhancement plus a part of prompt muons. From these quantitative analysis, it is concluded that prompt muons may contribute to the total flux in the energy range between several TeV and several hundreds of TeV but are not beyond the maximum prediction.

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Riassunto Si calcola il flusso di muoni pronti dei raggi cosmici che derivano da particelle cariche che sono prodotte in processi sia diffrattivi che non diffrattivi di collisioni primariearia. Si stima il suo contributo massimo sottolineando il carattere diffrattivo delle particelle con charm prodotte. Si confrontano i risultati osservati sulle distribuzioni angolari delle intensità muoni a una data profondità con i risultati calcolati. Non c'è una chiara evidenza per i muoni pronti. In un'analisi piú qualititativa si calcolano test χ² con riferimento alla forma prevista dello spettro muonico. La previsione è basata su una formula di Thompson e Walley per muoni che derivano dal decadimento di pioni e kaoni che mostra un incremento di sec θ piú una parte di muoni pronti. Da questa analisi quantitativa si conclude che i muoni pronti possono contribuire al flusso totale nell'intervallo di energia da alcuni TeV a parecchie centinaia di TeV ma non sono al di sotto della previsione massima.

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Резюме Вычисляется поток быстрых мюонов космических лучей, происходящих от очарованных частиц, которые были образованы в недифракционных и дифракционных процессах первичных соударений. Оценивается максимальная величина вклада быстрых мюонов, отмечая дифракционный характер образованных очарованных частиц. Мы сравниваем наблюденные результаты для угловых распределений мюонных интенсивностей на данной глубине с результатами вычислений. Не обнаружено явного подтверждения для быстрых мюонов. Проводится количественный анализ, χ² проверка ожидаемой формы мюонного спектра. Ожидаемая величина определяется из формулы Томпсона и Валлея для мюонов, возникающих из распадов пионов и каонов, которая обнаруживает sec θ возрастание плюс вклад от быстрых мюонов. На основании этого количественного анализа делается вывод, что быстрые мюоны могут давать вклад в полый поток в области энергий от нескольких ТэВ до нескольких сотен ТэВ.

     

Ultraslow polaron dynamics in low-doped manganites from (139)La NMR-NQR and muon spin rotation

We report a (139)La NMR investigation of low-doped insulating manganite samples (LaMnO(3+delta) and La(1-y)Ca(y)MnO(3+delta)) as a function of temperature. A volume fraction with fast nuclear relaxations was revealed by the inhomogeneous loss of the NMR signal over a broad temperature interval. Comparison with muon spin rotation data demonstrates that the wipeout of the (139)La signal is mainly due to slowly fluctuating electric field gradients. This provides strong evidence for the slow diffusion of lattice excitations, identified with Jahn-Teller small polarons.