Magnetic field effects on low dimensional electron systems: Luttinger liquid behaviour in a quantum wire

We discuss the effects of a strong magnetic field in quantum wires. We show how the presence of a magnetic field modifies the role played by electron electron interaction producing a strong reduction of the backward scattering corresponding to the Coulomb repulsion. We discuss the consequences of this and other effects of magnetic field on the Tomonaga-Luttinger liquids and especially on their power-law behaviour in all correlation functions. The focal point is the rescaling of all the repulsive terms of the interaction between electrons with opposite momenta, due to the edge localization of the electrons and to the reduction of the length scale. Because of the same two reasons there are some interesting effects of the magnetic field concerning the backward scattering due to the presence of one impurity and the corresponding conductance. As an effect of the magnetic field we find also a spin polarization induced by a combination of electrostatic forces and the Pauli principle, quite similar to the one observed in large Quntum Dots.     

Magnetic susceptibility and short-range order in iron pnictides: Anisotropic J1-J2 Heisenberg model

The electron spin relaxation times by piezoelectric and polar optical phonon scattering in GaAs are calculated using the formula derived from the projection-reduction method. The temperature, magnetic field, and electron density dependences of the relaxation time are investigated. The electrons are found to be scattered mostly by piezoelectric phonons at low temperatures and polar optical phonons at high temperatures. The electron density affects the magnetic field dependence of the relaxation time at low temperatures but have only slight affects at high temperatures.     

Effect of scattering processes on the dynamics of electrons in narrow energy bands

We have investigated the effect of a magnetic field and the degree of filling and width of the band on the scattering processes on the basis of the Hubbard method. The electrical conductivity tensor was calculated with account taken of damping processes. It is shown that the relaxation times depend essentially on the electron spin orientations. Theordering of the electron spins under the influence of the external magnetic field leads to an increase of the electrical conductivity tensor, that in turn leads to a negative magnetoresistance.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 65–69, June, 1976.     

Vortex structures in nano-scaled superconducting networks

Using the de Gennes–Alexander equation, we have investigated the stable vortex structures in finite superconducting networks (10 × 10 holes) with disordered wires under an external magnetic field. Vortex structures change gradually with increasing magnetic field. For the network with a disordered wire at the edge, vortices are not pinned disordered hole, but enter into the network at the holes with the disorder. But for the network with two disordered wires, the vortex enters at the hole between two disordered wires. This behavior can be considered as the result of the nonlocality of superconductivity.     

Effect of magnetic impurities on energy exchange between electrons

In order to probe quantitatively the effect of Kondo impurities on energy exchange between electrons in metals, we have compared measurements on two silver wires with dilute magnetic impurities (manganese) introduced in one of them. The measurement of the temperature dependence of the electron phase coherence time on the wires provides an independent determination of the impurity concentration. Quantitative agreement on the energy exchange rate is found with a theory by G?ppert et al. that accounts for Kondo scattering of electrons on spin-1/2 impurities.     

The oscillatory galvanomagnetic size-effect in multilayered structures

Within the framework of the modified semi-classical Fuchs-Sondheimer model, we investigated theoretically the electrical resistivity of multilayered structures (MLS) consisting of alternating metallic layers (of different purity and different thicknesses) in a transverse magnetic field as functions of the ratio of the adjacent layer thicknesses and the magnetic field value. We have derived both a general formula (valid at arbitrary values of layer thicknesses) and asymptotic expressions that are valid when metallic layers are thick or thin compared with the electron mean free path. We found a non-monotonic behavior in the resistivity vs. the value of an applied magnetic field. As we demonstrated, this behavior is sensitive to the characteristics of the electron scattering in the interlayer interfaces in low magnetic fields. Moreover, the MLS resistivity oscillates in high magnetic fields with the field value (or with the layer thicknesses). The oscillation includes the harmonics that correspond both to the each layer thicknesses and the total thickness. The intensity of the oscillation is determined by the diffusive electron scattering in the interfaces, and the oscillation amplitude is proportional to the coefficient of the electron transmission through the interlayer interfaces. We have calculated numerically the resistivity in a wide range of fields and layer thicknesses at various values of the parameters of the interface and bulk electron scattering.      

Transient response of hot electrons in narrow-gap semiconductors at low temperatures in the presence of a longitudinal quantizing magnetic field

Transient response of hot electrons in narrow-gap semiconductors to a step electric field in the presence of a longitudinal quantizing magnetic field has been studied at low temperatures using displaced Maxwellian distribution. The energy and momentum balance equations are used assuming acoustic phonon scattering via deformation potential responsible for the energy relaxation and elastic acoustic phonon scattering together with ionized impurity scattering for momentum relaxation. The calculations for the variation of drift velocity and electron temperature as functions of time are made for n-Hg_0.8Cd_0.2 Te in the extreme quantum limit at 1.5 K and 4.2 K. The momentum and energy relaxation times are found to be of the same order of magnitudes as with the experimental values. The magnetic field and lattice temperature dependences of the relaxation rates have been investigated.One of the authors, Suchandra Bhaumik, acknowledges the Council of Scientific and Industrial Research (New Delhi) for financial support.     

Optical coherent transient effects in a magnetized semiconductor quantum wire

Effects of an external magnetic field on free induction decay (FID) and the Stark effect in GaAs/GaAlAs quantum wires have been investigated analytically. Our results show that both FID and the Stark effect become enhanced due to the presence of a magnetic field. We have also seen that the magnetic field plays an important role in wider wires while in thinner wires, the geometric confinement dominates over the magnetic effects. The results are found to be in good qualitative agreement with that available in the literature.     

Electron relaxation mechanisms in n-Bi-Sb semiconducting alloys

The magnetic field dependence of diffusion thermal electromotive force α₂₂(H) (?T ∥ C ₁) in degenerate n-Bi-Sb semiconducting alloys, in which only L electrons participate in transfer phenomena, had a maximum at H ∥ C ₃. The electron relaxation time was determined from the magnetic field value corresponding to this maximum. The dependences of the electron relaxation time on temperature and the concentration of alloy components and the dopant (on the concentration of electrons) were used to separate electron relaxation time components corresponding to scattering by phonons, ionized impurities, and component concentration fluctuations. The latter (“alloy”) mechanism of electron scattering by concentration fluctuations was for the first time considered for Bi-Sb alloys; its contribution was found to be comparable with those of the other scattering mechanisms. The obtained relaxation times were used to calculate theoretical magnetic field dependences of thermal electromotive force and the Nernst-Ettingshausen coefficient. The calculation results were in satisfactory agreement with experiment.     

A systematic study of the electron mobility in V-shaped quantum wires at low temperatures

We present a systematic study of the electron mobility in V-shaped AlGaAs/GaAs quantum wires taking into account the impurity (background, remote and interface) and the acoustic-phonon scattering. The electron scattering rates are calculated for wires with electron concentrations up to 10⁶ cm⁻¹ and temperatures up to 40 K by using Fermi’s golden rule. The effects of the interface roughness scattering and the alloy scattering are also discussed. The energy eigenstates and eigenvalues of the system under study are calculated using a finite difference method. We analyze the importance of each scattering mechanism on the mobility of several quantum wires of different qualities as a function of the electron concentration and the temperature.     

Surface-induced structural modification in ZnO nanoparticles

Cobalt?Ccobalt carbide [Co _x C (x?=?2 or 3)] and cobalt (FCC-Co) microwires have been synthesized using a polyol method in the presence of a high external magnetic field of 4.3?kOe. It was reported before that the synthesis of these particles in the absence of magnetic field leads to the formation of spherical particles. Analysis of the X-ray diffraction (XRD) scans indicates that the synthesized Co _x C wires consist of four phases?? ??-Co, ??-Co, Co₃C, and Co₂C. The percent composition of these phases was 53.3?% Co₃C, 26.8?% Co₂C, 12.5?% ??-Co, and 7.4?% ??-Co. XRD analysis of the as-synthesized cobalt wires shows that it consists of single-phase FCC-Co. Based on Scherrer analysis of the XRD data, the average crystallite sizes of the cobalt carbide and the cobalt particles are 18.5 and 16.3?nm, respectively. Scanning electron microscopy (SEM) studies show that the diameter of Co _x C wires is in the range of 1.6(±0.2)???m with their length varying between 18 and 30???m while the diameter of the cobalt wires is 1.65(±0.1). The SEM results infer that the morphology of the growing particles was controlled by the magnetic field with the applied field directs the growth of the particles into wires. The magnetic measurements indicate a superparamagnetic character of the cobalt wires and a soft ferromagnetic nature of the synthesized Co _x C chains. The degree and field range of the interactions between magnetic domains have been investigated using a Henkel plot.     

Time-resolved magneto-optical properties of InxGa1−xAs V-shaped single quantum wires

In this work we present a time-resolved magneto-luminescence investigation (up to 8 T) of InGaAs V-shaped quantum wires (QWRs) with different In content, as a function of temperature and the applied magnetic field. The states of the wires were investigated by CW PL and quantitatively compared with the results of a numerical solution of the two-dimensional Schrodinger equation. Time-resolved experiments performed in magnetic field at different temperatures indicate the existence of a competition between the electron confinement occurring in deep QWRs at low temperature, and the magnetic confinement prevailing in shallower QWRs.     

Measuring magnetic fields in plasmas by means of light scattering

The theory of light scattering in plasmas containing a magnetic field yields the special case of modulated scattering spectra. The modulation frequency is governed by the field in the plasma and is equal to the electron cyclotron frequency. In this investigation magnetic fields in a plasma were determined by a laser scattering experiment. The experimental data were: electron densityn _e=10¹⁶cm^?3, electron temperatureT _e=3.2 eV, scattering angle θ=90 °, scattering parameter α=0.6, and a maximum field in the plasma of 125 kG. The spectrum measured at the maximum magnetic field was modulated with 3.6 × 10¹¹ Hz. In scattering experiments with a field reduced by about 20% the observed modulation frequency was 2.8 × 10¹¹ Hz. A thermal spectrum with a smooth profile was found when no field was present in the plasma. Applying the theory of cyclotron modulated spectra one obtains from the scattering experiment magnetic fields of 128, 100, and 0 kG. Within the experimental accuracy these values agree well with the fields determined by means of magnetic probes. Other possible interpretations of the measured deviations from thermal spectra (modulation with the plasma frequency or additional cold electron components in the plasma) are discussed, but they afford no explanation. This experiment has domonstrated that magnetic fields in plasmas can be measured locally and almost without disturbance by means of light scattering.     

Effects of external magnetic field on the electron Zitterbewegung in the quantum dots and wires with Rashba spin–orbit interaction

We study in this article the effects of external magnetic field on the electron Zitterbewegung in semiconductor quantum dots and wires with parabolic confinements and Rashba spin–orbit interaction. In doing so, we have calculated the dynamics of the expectation value of the position operator by means of the time evolution operator in an appropriate Hilbert space. The results show that the electron Zitterbewegung, its amplitude which is related to the electron confinement, and the period of the electron Zitterbewegung depend on the external magnetic field. We propose that the magnetic field can be used as an external agent to control the electron Zitterbewegung, a fundamental key for experimental detection of this phenomena.     

Sample size dependence of magnetoconductance fluctuations in narrow n+-GaAs wires

Submicron sized n⁺-GaAs wires are fabricated using MOCVD and electron beam lithography techniques, and effects of sample size on magnetoconductance fluctuations have been investigated. It is found that the magnitude of the fluctuation decreases by ensemble averaging with increasing sample size in wires with the width and the length larger than the inelastic scattering length. It is found that the fluctuation becomes larger than the predicted value in wires with the width narrower than the scattering length.     

Effects of inhomogeneous magnetic fields on the electron transport through a quantum-wire system

The electron transport through a quantum-wire system in the presence of inhomogeneous magnetic fields is investigated theoretically. The system consists of two parallel quantum wires coupled by two ballistic windows, while the magnetic fields applied are uniform and equal in the two wires but vanishing in the two coupling windows and everywhere between the wires. Various transmissions of the system are calculated. It is found that the inhomogeneous magnetic fields induce irregular transmission oscillations in the low and moderate magnetic-field regions, and regular ones in the high field region. These transmission oscillations are due to interference between the electron waves traveling through different coupling windows and can be interpreted in terms of a semiclassical model. The Hall resistance of the system is also calculated and is found to show similar regular oscillations at high magnetic fields.     

0.7 Structure and zero bias anomaly in ballistic hole quantum wires

We study the anomalous conductance plateau around G=0.7(2e2/h) and the zero bias anomaly in ballistic hole quantum wires with respect to in-plane magnetic fields applied parallel B parallel and perpendicular B perpendicular to the quantum wire. As seen in electron quantum wires, the magnetic fields shift the 0.7 structure down to G=0.5(2e2/h) and simultaneously quench the zero bias anomaly. However, these effects are strongly dependent on the orientation of the magnetic field, owing to the highly anisotropic effective Landé g-factor g* in hole quantum wires. Our results highlight the fundamental role that spin plays in both the 0.7 structure and zero bias anomaly.     

多光子非线性Compton散射对等离子体中电子运动的影响

应用多光子非线性Compton散射模型,研究了多光子非线性Compton散射对激光等离子体中电子运动的影响,提出了将入射激光和Compton散射光形成的耦合光、耦合光与等离子体产生的自生磁场形成的混合场作为加速电子的新机制,对电子动量和能量方程进行了修正和数值模拟。结果表明,当混合场的电场振幅与磁场振幅相等时,回旋共振电子在与混合场作用时间内能被加速到很高的能量;电子加速能量随耦合光幅值的增大而增大,随电子耦合初始角度的增大而周期变小,随电子横向耦合归一化初始速度的增大,开始时较快增加,之后缓慢增加,最后趋于稳定。     

Electron scattering with spin flip in indium antimonide and indium arsenide

The longitudinal magnetoresistance has been investigated at temperatures in the range from 2.8 to 200 K in a magnetic field of up to 200 kOe with the aim of determining the temperature range and the magnetic field strength at which charge carrier scattering with spin flip occurs in n-type indium arsenide and n-type indium antimonide. It is established that quantum oscillations of the longitudinal magnetoresistance of indium arsenide exhibit weak zero maxima due to electron scattering with spin flip at temperatures in the range from 4 to 35 K in a magnetic field of 146 kOe. For the longitudinal magnetoresistance of indium antimonide, zero maxima caused by electron scattering with spin flip are revealed in the temperature range from 60 to 80 K in a magnetic field of 132 kOe.