GaN/AlxGa1-xN异质结二维电子气的磁电阻研究

通过对GaN/Al_xGa_1-xN异质结中二维电子气磁输运结果的分析,研究了磁电阻的起因.结果表明,整个磁场范围的负磁电阻是由电子-电子相互作用引起的,而高场下的正磁电阻来源于平行电导的进一步修正.用拟合的方法得到了电子-电子相互作用项以及平行电导层的载流子浓度和迁移率,并用不同的计算方法对拟合结果进行了验证.     

La1-xPrxMnO3(x=0.1,0.2)薄膜庞磁电阻性质的研究

一种新的庞磁电阻氧化物薄膜La1-xPrxMnO3(x=0.1,0.2)薄膜用脉冲激光沉积(PLD)方法生长在(100)SrTiO3单晶基底上.XRD结果显示薄膜具有很好的外延单晶取向.电输运和磁性质的研究表明薄膜具有显著的庞磁电阻效应(CMR)效应,其中磁电阻比率达95%(在5T的磁场下).X射线光电子能谱(XPS)的结果表明薄膜体系中Pr离子的价态为+4价,因此该薄膜很可能是电子掺杂的庞磁电阻体系.     

稀土掺杂锰氧化物庞磁电阻效应

过去十多年来，具有庞磁电阻效应的稀土掺杂锰氧化物成为了凝聚态物理研究的重要领域。锰氧化物的载流子自旋极化率高，且在居里温度附近表现出很大的磁电阻效应，因此在自旋电子学中有潜在的应用前景。另一方面，锰氧化物是典型的强关联电子体系，它对目前有关强关联体系的认识提出了很大挑战。本文综述了锰氧化物的各种性质及其物理原因。全文首先概述了锰氧化物的庞磁电阻效应及其晶格和电子结构，简单介绍了其他一些庞磁电阻材料；随后综述了锰氧化物的电荷／轨道有序相及其输运性质；在第四部分简单介绍了锰氧化物中庞磁电阻效应的机制；最后讨论了锰氧化物的一些可能的应用，如低场磁电阻效应、磁隧道结、磁p-n结以及全钙钛矿的场效应管和自旋极化电子注入装置等。     

La1－xPrxMnO3(x=0.1，0.2)薄膜庞磁电阻性质的研究

一种新的庞磁电阻氧化物薄膜La_1-xPr_xMnO₃(x=0.1，0 .2)薄膜用脉冲激光沉积(PLD)方法生长在(100)SrTiO₃单晶基底上.XRD结果显示 薄膜具有很好的外延单晶取向.电输运和磁性质的研究表明薄膜具有显著的庞磁电阻效应(CM R)效应，其中磁电阻比率达95％(在5T的磁场下).X射线光电子能谱(XPS)的结果表明薄膜体 系中Pr离子的价态为+4价，因此该薄膜很可能是电子掺杂的庞磁电阻体系. 关键词： 脉冲激光沉积 1-xPr_xMnO₃')" href="#">La_1-xPr_xMnO₃ 电子 掺杂 庞磁电阻     

非磁性半导体异常磁电阻效应的有效介质理论

有效介质理论自洽方程被用来研究非磁性半导体材料的异常磁电阻效应. 通过建立两组分无序电导网络,同时引入组分的霍尔效应,计算了体系的有效电导张量随磁场和组分浓度的变化关系.结果表明,当两种组分具有不同类型的载流子时,体系中各组分零场电阻的差异将导致在垂直磁场和平行磁场方向上产生异常的磁电阻效应.这些宏观的磁电阻效应来源于体系中的非均匀性,并与组分的几何逾渗结构具有明显的关联. 关键词： 异常磁电阻效应 非磁性半导体 有效介质近似     

自旋输运和巨磁电阻--自旋电子学的物理基础之一

介绍磁性纳米结构和锰氧化物中电子的自旋极化输运和巨磁电阻效应，它们是新近发展的自旋电子学的物理基础之一．着重讨论的是以下三方面的基本物理图像：磁多层结构的巨磁电阻，铁磁隧道结的隧穿磁电阻，掺杂锰氧化物的庞磁电阻效应．     

In0.53Ga0.47AS/In0.52Al0.48As量子阱中的正磁电阻效应

在低温强磁场条件下,对In0.53 Ga0.47 As/In0.52AI0.48As量子阱中的二维电子气进行了磁输运测试.在低磁场范围内观察到正磁电阻效应,在高磁场下这一正磁电阻趋于饱和,分析表明这一现象与二维电子气中的电子占据两个子带有关.在考虑了两个子带之间的散射效应后,通过分析低磁场下的正磁电阻,得到了每个子带电子的迁移率,结果表明第二子带电子的迁移率高于第一子带电子的迁移率.进一步分析表明,这主要是由两个子带之间的散射引起的.     

In0.53Ga0.47As/In0.52Al0.48As量子阱中的正磁电阻效应

在低温强磁场条件下,对In_0.53Ga_0.47As/In_0.52Al_0.48As量子阱中的二维电子气进行了磁输运测试.在低磁场范围内观察到正磁电阻效应,在高磁场下这一正磁电阻趋于饱和,分析表明这一现象与二维电子气中的电子占据两个子带有关.在考虑了两个子带之间的散射效应后,通过分析低磁场下的正磁电阻,得到了每个子带电子的迁移率,结果表明第二子带电子的迁移率高于第一子带电子的迁移率.进一步分析表明,这主要是由两个子带之间的 关键词： 二维电子气 正磁电阻 子带散射     

磁电子学讲座 第八讲 磁电子学——一门新型交叉学科

简要介绍磁电子学的基本概念、研究对象、应用背景．重点介绍自旋极化电子在人工结构材料中的一些特殊输运性质，例如，巨磁电阻效应、磁隧道效应、自旋极化电子的注入效应、沟道效应，以及依据这些效应和特性做成的各种新型电子器件的原理，例如，计算机磁头、磁随机存储器（ＭＲＡＭ）、自旋开关三极管、铁电场效应三极管、电流放大器和逻辑元件等．     

电子-声子相互作用对平行双量子点体系热电效应的影响

量子点体系是一种典型的低维体系, 该体系的独特物理特性有利于提高热电转换效率. 本文采用非平衡态格林函数方法, 选择平行双量子点结构, 详细讨论了电子-声子相互作用对该体系的电导、热电功率、热电优值以及热导等热电效应相关参数的影响, 全面描述了电子-声子相互作用对该结构中热电效应的影响. 理论计算结果表明, 在低温情况下, 该体系中的法诺干涉能够有效增强热电效应, 而电子-声子相互作用通过破坏法诺干涉而在一定程度上抑制电导以及热导过程. 然而, 电子-声子相互作用不会显著地影响热电功率的幅值, 并且热电优值的极值几乎不会改变, 因此在低温条件下电子-声子相互作用并不是破坏量子点体系热电效应的必要条件. 本文的结果将有利于澄清电子-声子相互作用对量子点体系热电效应的影响.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.