Full counting statistics of spin currents

We discuss how to detect fluctuating spin currents and derive full counting statistics of electron spin transfers. We consider several detectors in series monitoring different components of the spins. We have found that in general the statistics of the measurement outcomes cannot be explained with the projection postulate and essentially depends on the quantum dynamics of the detectors.     

Electron-spin polarization in a non-magnetic heterostructure

The spin dependent electron transmission through a non-magnetic III-V semiconductor symmetric well is studied theoretically so as to investigate the output transmission current polarization at zero magnetic field. Transparency of electron transmission is calculated as a function of electron energy as well as the well width, within the one electron band approximation along with the spin-orbit interaction. Enhanced spin-polarized resonant tunneling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level is observed. We predict that a spin-polarized current spontaneously emerges in this heterostructure. This effect could be employed in the fabrication of spin filters, spin injectors and detectors based on non-magnetic semiconductors.     

Spin dependent mean-free path of low-energy electrons in ferromagnetic materials

Spin resolved attenuation measurements of electrons transmitted through overlayers of Fe and Co show that the electron inelastic mean free path (IMFP) in these materials is spin-dependent at low energies. The spin-up IMFP is larger than the spin-down IMFP. The values from different studies are in reasonable agreement. The data suggest that the origin of the spin dependence is mainly due to inelastic processes. Effects from spin dependent elastic scattering have not been identified directly in these experiments. The spin filter effect based on preferential attenuation of spin-down electrons can be used as a basis of spin polarization detectors.     

Detection of spin-polarized electrons injected into a two-dimensional electron gas

The spin-dependent mean-free path of electrons in a high-mobility InAs two-dimensional electron gas (2DEG) is measured. Ferromagnetic metal/insulator/2DEG junctions are fabricated on a common channel in a nonlocal geometry and used as spin injectors and detectors. For electrons in spin-orbit eigenstates at 4.5 K, lower bounds for the spin mean-free path and relaxation time are Lambda(S) > or = 4.6 microm and tau(s) > or = 3.8 ps, respectively. The temperature dependence is weak over the range 4.5相似文献   

Complete Deterministic Analyzer for Multi-Electron Greenberger–Horne–Zeilinger States Assisted by Double-Side Optical Microcavities

We present a complete deterministic scheme for the multi-electron Greenberger–Horne–Zeilinger (GHZ) state analyzer, resorting to an interface between the polarization of a probe photon and the spin of an electron in a quantum dot embedded in a double-sided optical microcavity. All the multi-spin GHZ states can be completely discriminated by using single-photon detectors and linear optical elements. Our scheme has some features. First, it is a complete GHZ-state analyzer for multi-electron spin systems. Second, the initial entangled states remain after being identified and they can be used for a successive task. Third, the electron qubits are static and the photons play a role of a medium for information transfer, which has a good application in quantum repeater in which the electron qubits are used to store the information and the photon qubits are used to transfer the information between others.     

Reprint of : Transient dynamics of spin-polarized injection in helical Luttinger liquids

We analyze the time evolution of spin-polarized electron wave packets injected into the edge states of a two-dimensional topological insulator. In the presence of electron interactions, the system is described as a helical Luttinger liquid and injected electrons fractionalize. However, because of the presence of metallic detectors, no evidences of fractionalization are encoded in dc measurements, and in this regime the system does not show deviations from its non-interacting behavior. Nevertheless, we show that the helical Luttinger liquid nature emerges in the transient dynamics, where signatures of charge/spin fractionalization can be clearly identified.     

Effect of electron-electron interaction on spin relaxation of charge carriers in semiconductors

An analysis of spin dynamics is presented for semiconductor systems without inversion symmetry that exhibit spin splitting. It is shown that electron-electron interaction reduces the rate of the Dyakonov-Perel (precession) mechanism of spin relaxation both via spin mixing in the momentum space and via the Hartree-Fock exchange interaction in spin-polarized electron gas. The change in the Hartree-Fock contribution with increasing nonequilibrium spin polarization is analyzed. Theoretical predictions are compared with experimental results on spin dynamics in GaAs/AlGaAs-based quantum-well structures. The effect of electron-electron collisions is examined not only for two-dimensional electron gas in a quantum well, but also for electron gas in a bulk semiconductor and a quantum wire.     

Comparative analysis of pulsed electron spin resonance spectrometers at X-band and S-band

Comparative analysis of pulsed electron spin resonance spectroscopy at X-band and at S-band indicates that despite the lower sensitivity at the lower frequency, electron spin echo spectroscopy at S-band provides valuable information on the electron-nuclear interactions in systems where the electron spin echo modulation is too small to study well at X-band. It is shown that independent experimental data on electron spin echo modulation and decay at both X-band and S-band put additional constraints on the structural parameters obtained by comparison of experimental and simulated nuclear modulation patterns, and can also help to elucidate the electron spin relaxation mechanism.     

Electron spin resonance of magnetic ions in metals an experimental review

The contribution that the technique of electron spin resonance has made to our understanding of the behaviour of localized moments in metals is reviewed. The main areas of application of the technique are discussed at a simple theoretical level and its limitations are pointed out. A comprehensive review of the experimental results obtained from electron spin resonance is presented and, in appendices to the article, a comprehensive list of experimental results is given indexed to author, impurity and host and to areas of application. In a final section of the review an attempt is made to suggest those areas in which electron spin resonance still has an important part to play in adding to our understanding of magnetism in metals.     

Efficient Preparation and Nondestructive Analysis of Photon and Spin Entangled States with Double-Sided Cavity and Nitrogen-Vacancy Center Coupled System

In this paper, we study the preparation and nondestructive analysis of photon and spin entangled states with double-sided cavity and nitrogen-vacancy center coupled system, which is efficient in weak-coupling regime. The setups are based on some simple linear optical elements, delay lines and conventional photon detectors, which are feasible with existing experimental technology. Numerical simulation demonstrates that all protocols’ fidelities and successful probabilities are high in principle. Therefore, our protocols may be useful for decreasing the experimental requirements for preparation and nondestructive analysis of entangled states.     

Characterization of semiconductor detectors of (1–30)-keV monoenergetic and backscattered electrons

Semiconductor detectors of backscattered electrons are basic elements of all modern scanning electron microscopes. Their quality is determined by the properties of planar p-n junctions and the parameters of the protective layer on the detector surface. The main characteristics of semiconductor detectors are considered, their response functions are calculated, and the threshold signal cutoff energies are found both for a monoenergetic electron beam and for detection of the total energy spectrum of backscattered electrons. The experimental results are in good agreement with the computational model data.     

Recent results from digital INGA at BARC–TIFR Pelletron Linac Facility and future plans

An experimental campaign aimed at studying various high spin phenomena using the Indian National Gamma Array (INGA) at the BARC–TIFR Pelletron Linac Facility has been successfully completed. The array consisting of a large number of Compton-suppressed clover detectors was coupled to a digital data acquisition system with 96 channels. The present system provides higher throughput, better energy resolution and better stability of gain for the multidetector Compton-suppressed clover array compared to its previous conventional system with analog shaping. Selected results from this array are discussed which highlight the exotic shapes, novel excitation modes and interesting isomers of the nuclei. The preliminary results from the experimental efforts to improve the sensitivity and capability of the array by adding ancillary detectors are also described briefly.     

Ultrafast electron spin dynamics in bulk CdTe investigated by femtosecond pump-probe reflection spectroscopy

The transient spin polarization dynamics in bulk cadmium telluride (CdTe) at 70 K is investigated by the circularly polarized pump-probe reflection technique. A general expression is derived from the rate equations of a two-level system with small signal approximation to describe the light-helicity-dependent reflection spectrum. The initial degree of electron spin polarization in the excited state and the electron spin relaxation time in bulk CdTe at low temperature with different carrier density are analyzed according to this model. Our experimental results reveal that the D?yakonov–Perel? mechanism based on a fully microscopic kinetic spin Bloch equation (microscopic KSBE) approach dominates in the electron spin relaxation process in bulk CdTe crystal.     

Room temperature electrical detection of spin coherence in C60

An experimental demonstration of electrical detection of coherent spin motion of weakly coupled, localized electron spins in thin fullerene C60 films at room temperature is presented. Pulsed electrically detected magnetic resonance experiments on vertical photocurrents through Al/C(60)/ZnO samples showed that an electron spin Rabi oscillation is reflected by transient current changes. The nature of possible microscopic mechanisms responsible for this spin to charge conversion as well as its implications for the readout of endohedral fullerene (N@C(60)) spin qubits are discussed.     

Phonon-mediated electron-spin phase diffusion in a quantum dot

An effective spin relaxation mechanism that leads to electron spin decoherence in a quantum dot is proposed. In contrast with the common calculations of spin-flip transitions between the Kramers doublets, we take into account a process of phonon-mediated fluctuation in the electron spin preces-sion and subsequent spin phase diffusion. Specifically, we consider modulations in the longitudinal g factor and hyperfine interaction induced by the phonon-assisted transitions between the lowest electronic states. Prominent differences in the temperature and magnetic field dependence between the proposed mechanism and the spin-flip transitions are expected to facilitate its experimental verification. Numerical estimation demonstrates highly efficient spin relaxation in typical semiconductor quantum dots.     

双次曝光积分效应实现杂质浓度分布均匀化

激光诱导扩散中,当入射激光光强为高斯分布甚至均匀分布时，微小扩散区的温度分布不均匀。由于扩散系数是温度的函数，必将导致扩散后杂质浓度分布的均匀性较差，无法制作出高性能的p-n结。提出采用多次激光诱导扩散的积分效应来实现杂质浓度分布的均匀化整形。对于InP衬底的CO2激光诱导Zn扩散,利用温度闭环测控系统测得的基片表面热斑温度场分布，分析计算了两次激光诱导扩散重叠区域的浓度分布积分效应。在此基础上模拟计算出，用双次曝光积分效应做杂质浓度分布的均匀化整形时，基片上两次激光照射位置的最佳间隔为20 μm。这为改进激光诱导扩散工艺，用多次曝光实现面均匀的杂质浓度分布奠定了理论基础。     

Outer-sphere nuclear spin relaxation in paramagnetic systems: a low-field theory

A low-field theory for paramagnetic relaxation enhancement (PRE), appropriate for the outer-sphere relaxation, is presented for the electron spin quantum number S = 1, 3/2, 2, 5/2, 3 and 7/2. The theory is used to calculate the PRE at low magnetic field, as a function of the translational diffusion coefficient, for various values of the electron spin quantum number, for small and fairly large values of the static zero-field splitting (ZFS), and for a given set of parameters determining the electron spin relaxation. We have found earlier that the static ZFS has a profound influence on the electron spin relaxation; such effects are also evident in the present study. Comparisons are made with other existing models for the outer-sphere PRE, and significant differences are found for slowly diffusing systems with large ZFS. The theory is also used to obtain a novel interpretation of experimental data for an acetone solution of a Mn(III) complex.     

Highly spin-polarized room-temperature tunnel injector for semiconductor spintronics using MgO(100)

The spin polarization of current injected into GaAs from a CoFe/MgO(100) tunnel injector is inferred from the electroluminescence polarization from GaAs/AlGaAs quantum well detectors. The polarization reaches 57% at 100 K and 47% at 290 K in a 5 T perpendicular magnetic field. Taking into account the field dependence of the luminescence polarization, the spin injection efficiency is at least 52% at 100 K, and 32% at 290 K. We find a nonmonotonic temperature dependence of the polarization which can be attributed to spin relaxation in the quantum well detectors.