Quantum Analytical Theory for Giant Magnetoresistance in Magnetic Multilayered Cylindrical Systems

Taking into account the quantum size effects and considering three types of scattering from bulk impurities,rough surface and rough interfaces, we use quantum-statistical Green's function approach and Kubo theory to calculate the electronic conductivity and the giant magnetoresistance in magnetic multilayered cylindrical systems. It is found that in the limit of weakly scattering from impurities surface and interfaces, the total conductivity is given by a sum of conductivities of all the subbands and two spin-channels. For each subband and each spin-channel the scattering rate due to the impurities, surface and interfaces is added up.

Spin-valley-dependent transport and giant tunneling magnetoresistance in silicene with periodic electromagnetic modulations

The transport property of electrons tunneling through arrays of magnetic and electric barriers is studied in silicene. In the tunneling transmission spectrum, the spin-valley-dependent filtered states can be achieved in an incident energy range which can be controlled by the electric gate voltage. For the parallel magnetization configuration, the transmission is asymmetric with respect to the incident angle θ, and electrons with a very large negative incident angle can always transmit in propagating modes for one of the spin-valley filtered states under a certain electromagnetic condition. But for the antiparallel configuration, the transmission is symmetric about θ and there is no such transmission channel. The difference of the transmission between the two configurations leads to a giant tunneling magnetoresistance （TMR） effect. The TMR can reach to 100% in a certain Fermi energy interval around the electrostatic potential. This energy interval can be adjusted significantly by the magnetic field and/or electric gate voltage. The results obtained may be useful for future valleytronic and spintronic applications, as well as magnetoresistance device based on silicene.

Negative magnetoresistance in Dirac semimetal Cd_(3)As_(2)with in-plane magnetic field perpendicular to current

Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negative magnetoresistance(negative MR)under parallel magnetic field and current has been used as a probable evidence ofWeyl fermions in recent years.Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd_(3)As_(2)nanowires.The negative MR has a considerable value of-16%around 1.5 K and could persist to room temperature of 300 K with value of-1%.The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly.Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR.Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.

Large positive magnetoresistance in photocarrier-doped potassium tantalites

We report on the high-field magnetotransport of KTaO_(3)single crystals,which are a promising candidate for study in the extreme quantum limit.By photocarrier doping with 360 nm light,we observe a significant positive,non-saturating,and linear magnetoresistance at low temperatures accompanied by a decreasing Hall coefficient.When cooling down to 10 K,the magnetoresistance value of KTaO_(3)(100)reaches~433%at a magnetic field of 12 T.Such behavior can be attributed to all the electrons occupying only the lowest Landau level in the extreme quantum limit.Light inhomogeneity may also contribute to large linear magnetoresistance.These results provide insights into novel magnetic devices based on complex materials and add a new family of materials with positive magnetoresistance.

Negative Magnetoresistance Behaviour and Variable Range Hopping Conduction in Insulating NbSi Amorphous Alloys at Very Low Temperature with aagnetic Field

We present results of an experimental study of magnetoresistance (MR) in insulating NbSi amorphous alloys sample showing Variable Range Hopping (VRH) conductivity. The MR is found to be negative in a wide range of low temperature (4.2-20 K) and in the range of moderate magnetic fields (0-4 T). We made tentative analysis using three theoretical models which are the model of quantum interference, the model of Zeeman effect and the model of localized magnetic

Anisotropies of the g-factor tensor and diamagnetic coefficient in crystal-phase quantum dots in InP nanowires

Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing.In this context,unveiling the fundamental parameters of the crystal phase structure is of much relevance for several applications.Here,we report on the anisotropy of the g-factor tensor and diamagnetic coefficient in wurtzite/zincblende(WZ/ZB)crystal-phase quantum dots(QDs)realized in single InP nanowires.The WZ and ZB alternating axial sections in the NWs are identified by high-angle annular dark-field scanning transmission electron microscopy.The electron(hole)g-factor tensor and the exciton diamagnetic coefficients in WZ/ZB crystal-phase QDs are determined through micro-photoluminescence measurements at low temperature(4.2 K)with different magnetic field configurations,and rationalized by invoking the spin-correlated orbital current model.Our work provides key parameters for band gap engineering and spin states control in crystal-phase low-dimensional structures in nanowires.

Optical properties of excitons in strained Ga_x In_1-x As/GaAs quantum dot: effect of geometrical confinement on exciton g-factor

Taking into account anisotropy, nonparabolicity of the conduction band, and geometrical confinement, we discuss the heavy-hole excitonic states in a strained GaxIn1-xAs/GaAs quantum dot for various Ga alloy contents. The strained quantum dot is considered as a spherical InAs dot surrounded by a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and Ga ion content is numerically measured. Interband optical energy with and without the parabolic effect is computed using structural confinement. The interband matrix element for different Ga concentrations is also calculated. The oscillator strength of interband transitions on the dot radius is studied at different Ga concentrations in the GaxIn1-xAs/GaAs quantum dot. Heavy-hole excitonic absorption spectra are recorded for various Ga alloy contents in the GaxIn1-xAs/GaAs quantum dot. Results show that oscillator strength diminishes when dot size decreases because of the dominance of the quantum size effect. Furthermore, exchange enhancement and exchange sDlitting increase as exciton confinement inereases.

Two-dimensional Sb net generated nontrivial topological states in SmAgSb_(2) probed by quantum oscillations

The REAgSb_(2)(RE = rare earth and Y) family has drawn considerable research interest because the two-dimensional Sb net in their crystal structures hosts topological fermions and hence rich topological properties. We report herein the magnetization and magnetotransport measurements of SmAgSb_(2) single crystal, which unveil very large magnetoresistance and high carrier mobility up to 6.2 × 10^(3)% and 5.58 × 10^(3)cm^(2)·V^(-1)·s^(-1), respectively. The analysis of both Shubnikov–de Haas and de Haas–van Alphen quantum oscillations indicates nontrivial Berry phases in the paramagnetic state while trivial Berry curvature in the antiferromagnetic state, indicating a topological phase transition induced by the antiferromagnetic order. It is also supported by the first-principles calculations. The results not only provide a new interesting topological material but also offer valuable insights into the correlation between magnetism and nontrivial topological states.

Magnetotransport through an Aharonov-Bohm ring with parallel double quantum dots coupled to ferromagnetic leads

Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper studies the mag- netotransport through an Aharonov-Bohm （AB） ring with parallel double quantum dots coupled to ferromagnetic leads. It calculates the transmission probability in both the equilibrium and the nonequilibrium case, analyses the conduc- tance and the tunnel magnetoresistance for various parameters, and obtains some new results. These results show that this system is provided with an excellent spin filtering property, and that a large tunnelling magnetoresistance and a negative tunnelling magnetoresistance can arise by adjusting relative parameters; these facts indicate that this system is a possible candidate for spin valve transistors, and has important applications in spintronics.

Magnetic-Field-Induced Phase Transition and a Possible Quantum Hall Effect in the Quasi-One-Dimensional CDW Organic Conductor HMTSF-TCNQ

In the Temperature-Pressure phase diagram, the quasi-one-dimensional conductor, HMTSF-TCNQ, the ground state at ambient pressure is an insulator of charge density wave (CDW) below 30 K, while it shows a good metallic nature at higher temperature. The CDW insulating state is suppressed by a pressure of 1 GPa, which is considered to be a quantum critical point. Neither at 0 - 0.5 nor 2 GPa but only around this critical point in pressure, field-induced phases appear from 0.2 T through 10 T, where Rxy is almost constant and Rxx is very low. These phenomena are achieved when the magnetic field is applied along the least conducting axis. The behaviors are consistent with a kind of Quantum Hall Effect (QHE). The field-induce phase accompanied by the QHE might be the field-induced CDW (FICDW) similar to that of FISDW, observed in (TMTSF)2X salts. This paper presents the latest result of the Hall effects reviewing the history of the authors’ work on this material from preliminary to the latest ones.

电力系统宽频宽动态电流量测技术研究综述

新型电力系统要求电流互感器具备宽频带、宽量程、高准确度性能,以满足电网呈现出的时频域宽动态、多参量等新特征。因此,从磁场传感的机理出发,对电流测量传感耦合原理简要介绍,分别阐述了这些技术的优缺点、拓扑结构。重点讨论了各类电流传感装置的结构特点、性能参数及量测性能优化方案,最后总结了目前亟待解决的问题、发展趋势和应用前景。光学电流互感器技术日趋成熟,应用广泛。基于NV色心的磁传感技术在测量性能方面已经超过传统传感器,配合光纤传感技术环境适应性强,电流测量领域前景广阔。

碳纳米管电磁量子性质的研究

对碳纳米管电磁特性的研究进展进行了系统的综述,并溶入我们最近对碳纳米管输运特性、本征电阻、磁阻等的研究结果,简洁地介绍了碳纳米管电磁量子特性研究的方法、理论、主要发现及意义.

巨磁电阻效应

介绍了巨磁电阻效应的概念和研究意义,对金属及其合金的磁电阻效应、负巨磁电阻效应以及正磁电阻效应产生的机理进行了简要分析,并展望了巨磁电阻效应未来的研究。

双量子环的隧穿电导和隧穿磁电阻

研究了双量子环的隧穿电导和隧穿磁电阻,研究结果表明:隧穿电导和隧穿磁电阻都随半导体环增大做周期性等幅振荡。δ势垒、Rashba自旋轨道耦合、AB磁通对隧穿电导或隧穿磁电阻的影响各不相同。隧穿磁电阻随AB磁通增强发生周期性等幅振荡,并随φ0角的减小而增大。两电极磁矩方向反平行时,隧穿磁电阻恒为零。

磁性多层膜研究进展:理论和实验

详细叙述了磁性多层膜研究的理论和实验进展，在不同的磁性多层膜材料中，大量实验事实证明和理论预示磁性多层膜具有独特的物理性质，如维度磁性、界面各向异性、耦合作用、巨磁阻、层间交换作用振荡和磁性量子隧道效应等等，因而，磁性多层膜是理论研究和技术应用的重要课题。

铋锑合金中Weyl费米子的磁输运性质研究

铋锑合金(Bi1-xSbx)的能带结构随x而变化,在拓扑绝缘体和拓扑半金属的研究中具有重要的地位。对Bi0.96Sb0.04的研究表明,该合金的电阻率随温度的升高先升后降,具有典型的半金属特点。在极低温度下可以观察到纵向磁电阻和横向霍尔电阻随外磁场的Shubnikov de Haas振荡,且两者的振荡相位正好相反。随磁场增加的不饱和线性磁电阻可以解释为在具有无能隙或极小能隙材料中,费米面附近电子线性色散关系带来的量子效应。在低温下,通过外加磁场可使简并的Dirac锥电子,分离成不同手性的Weyl电子,在磁场方向与电流方向一致时观察到了手性反常引起的负磁电阻效应。

Electronic transport properties of Co cluster-decorated graphene

Interactions of magnetic elements with graphene may lead to various electronic states that have potential applications.We report an in-situ experiment in which the quantum transport properties of graphene are measured with increasing cobalt coverage in continuous ultra-high vacuum environment. The results show that e-beam deposited cobalt forms clusters on the surface of graphene, even at low sample temperatures. Scattering of charge carriers by the absorbed cobalt clusters results in the disappearance of the Shubnikov–de Haas（Sd H） oscillations and the appearance of negative magnetoresistance（MR）which shows no sign of saturation up to an applied magnetic field of 9 T. We propose that these observations could originate from quantum interference driven by cobalt disorder and can be explained by the weak localization theory.

Calculation of the Zeeman-Fine Energies and the Spectrum with Doppler-Shift Correction of Atomic Lithium

We have calculated the Zeeman-fine energies of atomic Lithium (Li) by using the varying effective Landé g-factor method. We take the principle quantum number in the range;(2 ≤n ≤10 ). For this range we find 26 different energy values and 325 wavelengths some of which are the same. The Doppler shift is found to be Δλ=±0.004λ. The Doppler shift-corrected wavelengths are in perfect agreement with the observed (NIST) values for atomic Li.

多壁纳米碳管中的AAS效应研究

分析研究了多壁纳米碳管中的AAS效应.通过给出多壁纳米碳管中电子的多圈(通道)分波波函数的量子干涉模型,在AAS理论的框架下推出了多壁纳米碳管磁电阻的解析表达式.研究还发现由于多壁纳米碳管壁间的相互作用,多壁纳米碳管中电子的输运性质是扩散型的,存在着一个确定的相位相干长度.有限的相位相干长度用在磁电阻公式中可以解释最新的几个多壁纳米碳管中的磁电阻实验,如典型的负磁阻效应、磁电阻随外加磁场的高阶周期震荡等.

Calculation of the Effective G-Factor for the (ns²S_1/2)→(np²P_3/2)→(n's²S_1/2) Transitions in Hydrogen-Like Atoms and Its Application to the Atomic Cesium

We have calculated the effective g-factor for the transitions in hydrogen-like atoms and applied it to atomic cesium. We have identified that not only the g* factor in this case is an integer number g* = 1, but also the existence of possible entangled states related to the above tran-sitions. Furthermore we have used the above result to calculate the transition energies which are in complete agreement (within the 1% margin error). Such results can give access to the production of new laser lights from atomic cesium.