锯齿型石墨烯纳米窄带中量子霍尔体系的电场调控

应用含自洽格点在位库仑作用的Kane-Mele模型,研究锯齿型石墨烯纳米窄带平面内横向电场对边界带能带结构和量子自旋霍尔(QSH)体系的影响.研究结果显示,当电场强度较弱时,外加电场的方向可以调控自旋向下的两个边界带一起朝不同方向移动,导致波矢q=0.5处自旋向下的两个纯边界态的能量简并劈裂方向可由电场调控;当电场强度进一步增强到超过0.69 V/nm,自旋向下的两个边界带出现较大带隙,能带反转,而自旋向上的电子结构无能隙,系统呈现半金属性,同时QSH体系不再是B类.特别当电场强度为1.17 V/nm时,在自旋向下能带的能隙中,q=0.5处存在自旋向上的纯边界态,意味着在8格点边界处可以产生自旋向上的纯边界电流.当电场强度持续增加时,QSH系统从B类到C类经历3个阶段的变化.当电场强度超过1.42 V/nm后,自旋向上的两个边界带也出现能带反转,分别成为导带和价带,系统成为C类的普通量子霍尔体系.     

Superexchange-mediated magnetization dynamics with ultracold alkaline-earth atoms in an optical lattice

Superexchange and inter-orbital spin-exchange interactions are key ingredients for understanding(orbital) quantum magnetism in strongly correlated systems and have been realized in ultracold atomic gases.Here we study the spin dynamics of ultracold alkaline-earth atoms in an optical lattice when the two exchange interactions coexist.In the superexchange interaction dominating regime,we find that the time-resolved spin imbalance shows a remarkable modulated oscillation,which can be attributed to the interplay between local and nonlocal quantum mechanical exchange mechanisms.Moreover,the filling of the long-lived excited atoms affects the collapse and revival of the magnetization dynamics.These observations can be realized in state-dependent optical lattices combined with the state-of-the-art advances in optical lattice clock spectroscopy.     

旋涂法制备氧化锆介质层及其在薄膜晶体管中的应用

采用旋涂法制备了氧化锆介质层薄膜,重点讨论了退火温度以及旋涂转速对薄膜性能的影响及作用机制。研究发现高温后退火一方面使得氧化锆水合物脱水形成氧化锆,另一方面促使氧化锆薄膜结晶。此外,转速较高时,其变化对薄膜厚度及粗糙度无显著影响。当转速为5 000 r/min、退火温度为300℃时,制备的绝缘层厚度具有良好的厚度均匀性,粗糙度为0.7 nm,漏电流为3.13×10^-5 A/cm²（电场强度1 MV/cm）。最终,利用ZrO₂薄膜作为栅极绝缘层,在玻璃基板上制备了铟镓锌氧化物-薄膜晶体管（IGZO-TFT）,其迁移率为6.5 cm²/（V·s）,开关比为2×10⁴。     

关于二级相变中热力学物理量突变的分析与自旋链模拟

理论上对二级相变中热容、体膨胀系数、等温压缩系数三个热力学物理量的变化进行了分析,进而使用自旋链模型的基态能量和von Neumann熵随模型参数变化的突变行为对二级相变中这三个物理量的变化所引起的系统序变进行模拟,得到二级相变中热容、体膨胀系数、等温压缩系数的变化是由于系统内部微观上发生关联序变的结果。     

Step-shape angular spin distribution in layered systems by Fe Mössbauer spectroscopy: A general treatment

In the so-called ‘step-shape’ angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval Δφ centered at an angle φ₀. A general approach for deriving the two parameters φ₀ and Δφ via ⁵⁷Fe Mössbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture Δφ develops symmetrically versus a fixed direction φ₀ (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mössbauer γ-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture Δφ is changing but also the aperture center φ₀ is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture.     

Persistent spin current in a quantum wire with weak Dresselhaus spin——orbit coupling

The spin current in a parabolically confined semiconductor heterojunction quantum wire with Dresselhaus spin--orbit coupling is theoretically studied by using the perturbation method. The formulae of the elements for linear and angular spin current densities are derived by using the recent definition for spin current based on spin continuity equation. It is found that the spin current in this Dresselhaus spin--orbit coupling quantum wire is antisymmetrical, which is different from that in Rashba model due to the difference in symmetry between these two models. Some numerical examples for the result are also demonstrated and discussed.     

Dependences of spin polarization on the control parameters in the spin-polarized injection through the magnetic p-n junction

Effective spin-polarized injection from magnetic semiconductor (MS) to nonmagnetic semiconductor (NMS) has been highlighted in recent years. In this paper we study theoretically the dependence of nonequilibrium spin polarization (NESP) in NMS during spin-polarized injection through the magnetic p-n junction. Based on the theory in semiconductor physics, a model is established and the boundary conditions are determined in the case of no external spin-polarized injection and low bias. The control parameters that may influence the NESP in NMS are indicated by calculating the distribution of spin polarization. They are the doping concentrations, the equilibrium spin polarization in MS and the bias. The effective spin-polarized injection can be realized more easily by optimizing the above parameters.     

Measurement of the neutron beam polarization of BL05/NOP beamline at J-PARC

We measured the neutron beam polarization of the BL05/NOP (Neutron Optics and Physics) beamline at J-PARC with an accuracy of less than 10⁻³ using polarized ³He gas as a neutron spin analyzer. Precise polarimetry of the neutron beam is necessary to understand the beamline optics as well as for the asymmetry measurements of the neutron beta decay, which are planned in this beamline.     

自旋电子学和相干态

自旋电子学是近年来发展起来的一个新研究领域,它研究固体,特别是半导体中的电子自旋相干态,实验发现,自旋相干态能够保持足够长的时间（几百ps量级）,因此有可能用来制造一个固态的量子计算机,但是制造实际的自旋电子器件,首先需要解决的是将自旋极化电子（或穴穴）注入半导体中的方法和如何检测它们。     

Coherence and squeezing in superpositions of spin coherent states

We consider the superpositions of spin coherent states and study the coherence properties and spin squeezing in these states. The spin squeezing is examined using a new version of spectroscopic squeezing criteria. The results show that the antibuching effect can be enhanced and spin squeezing can be generated in the superpositions of two spin coherent states.