Temperature-controllable spin-polarized current and spin polarization in a Rashba three-terminal double-quantum-dot device

We propose a Rashba three-terminal double-quantum-dot device to generate a spin-polarized current and manipulate the electron spin in each quantum dot by utilizing the temperature gradient instead of the electric bias voltage. This device possesses a nonresonant tunneling channel and two resonant tunneling channels. The Keldysh nonequilibrium Green's function techniques are employed to determinate the spin-polarized current flowing from the electrodes and the spin accumulation in each quantum dot. We find that their signs and magnitudes are well controllable by the gate voltage or the temperature gradient. This result is attributed to the change in the slope of the transmission probability at the Fermi levels in the low-temperature region. Importantly, an obviously pure spin current can be injected into or extracted from one of the three electrodes by properly choosing the temperature gradient and the gate voltages. Therefore, the device can be used as an ideal thermal generator to produce a pure spin current and manipulate the electron spin in the quantum dot.     

Influence of local spin polarization to the Kondo effect

We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer an eigenstate as shown by variational calculations where the splitting of the local energy Δ = ɛ _d↑ − ɛ _d↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.      

磁量子结构中二维自旋电子的隧穿输运

研究了零偏压和偏置电压作用下磁量子结构中自旋电子的隧穿输运性质. 结果表明电子自旋 输运的性质不仅取决于磁量子结构的构型、入射电子的能量和波矢, 而且取决于偏置电压. 在零偏压下, 由等同的磁垒磁阱构成的磁量子结构不具有自旋过滤的特点, 而由不等同的磁 垒磁阱构成的磁量子结构却具有较好的自旋过滤特点. 偏置电压极大地改变了磁量子结构中 电子的极化程度, 使得电子隧穿等同的磁垒磁阱构成的磁量子结构的输运性质也显著地依赖 于电子的自旋指向.关键词：磁量子结构自旋电子隧穿输运自旋极化     

AB效应对自旋多端输运的影响

利用紧束缚近似和格林函数方法,研究了AB效应和AB环对电子自旋输运的影响.计算表明,当在AB环的不同位置上连接相同或不同属性的输出端时,在一些能量范围内,由不同的输出端所输出的自旋流的方向是相反的;当固定入射电子的能量时,在同一磁通范围,从两个输出端输出的自旋流属性也是相反的.从而,可以通过控制AB环的结构和环内的磁通在输出端得到不同属性的自旋流.关键词：自旋极化输运量子点极化率自旋流     

Hydrodynamic analysis of electrostatic counter-streaming instability in a spin-polarized electron–positron–ion plasma

In this study, we present linear analysis of electrostatic counter-streaming instability in spin-polarized electron–positron–ion (e-p-i) plasma. With the aid of the separate spin evolution-quantum hydrodynamic (SSE-QHD) model, we derive the dispersion relation of counter-streaming instability. We numerically solve the dispersion and find four wave solutions: Langmuir wave, positron acoustic mode, and two electron and positron spin-dependent waves. It is noted that coupling of streaming and spin effects excites Langmuir instability and positron acoustic mode instability. However, in the absence of spin effect, only Langmuir instability will survive in e-p-i plasma. We have also discussed the effects of positron concentration, streaming speed, and spin polarization on the real frequency of waves and the growth rate. The present study may be helpful for understanding longitudinal wave propagation and instabilities in dense magnetized environments.     

声表面波对GaAs(110)量子阱发光特性的调制

结合声表面波和光致发光谱在低温(15K)下对非故意掺杂的GaAs(110)量子阱结构的发光特性进行了研究.实验结果表明,由于声表面波的作用GaAs(110)量子阱的发光强度减弱,并且其对应的重空穴能级出现了分裂的现象,当施加的声波强度P_rf达到20dBm时,能级分裂ΔE达到了10meV.进一步讨论了声表面波对GaAs(110)量子阱圆偏振光自旋注入的影响.关键词：发光GaAs量子阱声表面波自旋极化     

Observation of Overhauser shift in a self-assembled InAlAs quantum dot

We report the polarization-dependent energy shift of excitonic emission in a self-assembled InAlAs/AlGaAs quantum dot (QD). The energy shift is well known as Overhauser shift and was observed in a naturally formed GaAs QD using monolayer fluctuation of a quantum well. However, there has been no observation so far in a self-assembled QD, which is suitable for formation of vertically coupled QDs. We demonstrate that the magnitude of the Overhauser shift is enhanced by the photo-injection of the highly polarized electron and is controllable by the polarization of the excitation light in a self-assembled InAlAs QD.     

Spin transport properties in a non-uniform quantum wire modulated by both Rashba and Dresselhaus spin–orbit couplings

Spin transport properties in a non-uniform quantum wire (QW) in the presence of both the Rashba and Dresselhaus spin–orbit couplings (SOCs) is investigated by using the non-equilibrium Green's function (NEGF) method combined with the Landauer Büttiker formalism. It is found that such a non-uniform quantum wire exhibits considerable spin polarization in its conductance in the influence of both the Rashba and Dresselhaus SOCs, and that the two SOCs' strengths strongly affect both the magnitude and sign of the electron spin polarization. Interestingly, the Rashba and Dresselhaus SOCs play the same modulating role in the electron spin polarization. The proposed nanostructure can potentially be utilized to devise an all-electrical spintronic device.     

InGaN薄膜中电子自旋偏振弛豫的时间分辨吸收光谱研究

采用飞秒时间分辨圆偏振光抽运-探测光谱对In_01Ga_09N薄膜的电子自旋注入和弛豫进行了研究.获得初始自旋偏振度约为02,此结果支持在圆偏振光激发下,重、轻空穴带的跃迁强度比为3∶1,而不支持1∶1或1∶094的观点同时获得自旋偏振弛豫时间为490±70ps,定性分析了自旋弛豫机理,认为BAP机理是电子自旋弛豫的主要机理.关键词：电子自旋InGaN自旋极化自旋弛豫