Effects of geometrical symmetry on the vortex in mesoscopic superconductors

We first systematically study the multivortex states in mesoscopic superconductors via self-consistent Bogoliubov-de Gennes equations. Our work focuses on how the geometrical symmetry affects the penetration and arrangement of vortices in mesoscopic superconductors and find that the key parameter determining the entrance of the vortex is the current density at the hot spots on the edge of sample. Through determining the spatial distribution of hot spots, the geometrical symmetry of the superconducting sample influences the nucleation and entrance of vortices. Our results propose one possible experimental approach to control and manipulate the quantum states of mesoscopic superconductors with their topological geometries, and they can be easily generalized to the confined superfluids and Bose-Einstein condensates.     

Composition-controlled exchange bias training effect in FeCr/IrMn bilayers

For FeCr/IrMn bilayers, the exchange bias training effect and the magnetization reversal mechanism are correlated to each other and depend on the composition of the ferromagnetic layer. For high Fe contents, the asymmetric magnetization reversal is observed. During the training effect, both exchange field and coercivity decrease monotonically, suggesting a type I training effect. For low Fe contents, the domain wall depinning takes place for the two hysteresis loop branches. Only exchange field diminution happens in the training effect. The coercivity almost does not change in the process, corresponding to a type II training effect. It is suggested that the motion of antiferromagnetic spins is modified by the magnetization reversal mechanism in the ferromagnetic layer.     

Efficient two-photon sensitized luminescence of europium （Ⅲ） complex based on hypersensitive transitions

Red frequency-upconversion fluorescence emission is observed in europium(Ⅲ) complex with encapsulating polybenzimidazole tripodal ligands, pumped with 930- and 1070-nm picosecond laser pulses. The lumines- cence of transition 5D0 →7F2 (612 nm) is induced by two-photon absorption of hypersensitive transitions 7F0 →5D2 (465 nm) and 7F1 →5D1 (535 nm). Analysis results suggest that the two-photon excitation strength of these hypersensitive transitions is increased dramatically owing to the C3 symmetry of the coordination field.     

Intravascular 3.0 T MRI Using an Imaging-Guidewire: a Feasibility Study in Swine

This study was to validate the feasibility of using a magnetic resonance imaging-guidewire (MRIG) for intravascular 3.0 T MR imaging of deep-seated arterial walls of large animals. The functionality of a 0.032-in. MRIG was evaluated and the signal-to-noise ratio (SNR) was calculated. Then, MRI of ten iliofemoral arteries of six pigs was acquired by MRIG and surface coil. The difference in the SNRs of the arterial walls between different coils was compared. Histology examined the potential thermal injuries of the imaged vessels. The MRIG functioned with the 3.0 T MR scanner. The average SNR of the arterial walls was significantly higher with the MRIG than with the surface coils (76.22 ± 34.76 vs. 12.63 ± 4.25, P < 0.01). Histology showed no evidence of thermal injuries at the vessel walls. This study validated the feasibility of generating intravascular 3.0 T MRI of deep-seated arterial walls in large animals, which should facilitate the translation of this technique from 1.5 to 3.0 T MR scanner.     

铁基超导体Minimum模型中的d波和扩展s波

对比研究了Minimum模型中d-波配对和扩展s-波配对的基本性质.结果表明,超导序参量按类BCS关系随温度变化,重整化参数t对超导有抑制作用,当t足够大时,超导消失,系统进入正常金属相.此外,讨论了超导序参量随不同参量的变化关系.对于d波,系统有稳定态;而对于扩展s波,系统则没有稳定态.     

氮化镓基发光二极管结构中粗化 p型氮化镓层的新型生长方法

提出了一种新型p型氮化镓粗化外延生长方法,这种生长方法的本质特征是利用低温生长的p型氮化镓作为粗化层的"晶籽"层,然后在这一层的基础上高温快速生长p型氮化镓,使粗化程度得到放大. 经实际制作尺寸为12 mil×10 mil的蓝光发光二极管器件并进行验证测试,与未进行p型氮化镓粗化的结果相比,通过这种方法粗化的发光二极管光通量可提升45%;结果同时表明,该方法有效解决了低温生长p型氮化镓带来的漏电流大,及预通镁源带来的前置电压高的问题. 关键词： 粗化 氮化镓 p型氮化镓 发光二极管     

在群论框架下电子三重态与声子耦合的理论研究

本文基于绝热近似和群论导出了电声耦合系统的哈密顿量的一般形式,讨论了电声耦合系统中的电子算符和活跃的声子模式. 应用幺正平移变换和能量最小化方法,进一步计算了正四面体群下T*(e+t₂)杨-泰勒系统中的激发态能量,从对称性的角度分析了T₁电子态的能级分裂以及晶格体系的对称性破缺,得出了对称性的破缺方式和电声耦合系统密切相关的结论. 结果表明:通过群论与对称性分析完全可以定性地解释由于电声耦合所造成的简并电子 关键词： 电声耦合 杨-泰勒畸变 活跃的杨-泰勒声子模式 电声耦合哈密顿量     

利用252 Cf快裂变室测量BC501A液闪探测器的相对探测效率和响应函数

本文利用²⁵²Cf快裂变室和多参数数据采集系统,逐事例的同时记录了自发裂变中子和瞬发伽马的飞行时间(TOF),脉冲形状甄别(PSD)和反冲能量(RE,裂变中子是通过测量反冲质子;瞬发伽马是通过测量康普顿反冲电子)三维信息.详细介绍了通过离线数据分析完全扣除三维信息中的伽马事例贡献,以获得Φ50.8 mm×50.8 mm的BC501A液闪探测器的相对探测效率和响应函数的方法.在不通过探测器响应函数进行数据转换的条件下,利用中子的能量直接确定了中子的有效测量阈值.得到的中子 关键词： 252Cf快裂变室')" href="#">²⁵²Cf快裂变室 BC501A液闪探测器 相对探测效率 响应函数     

Film thickness dependence of electro-optic effect in epitaxial BaTiO3 thin films

Based on the phenomenological Landau-Devonshire theory, we investigate the film thickness dependence of ferroelectric and electro-optic properties of epitaxial BaTiO₃ thin films grown on SrTiO₃ and MgO substrates. By using the effective substrate lattice parameter concept, the film thickness dependence of misfit strain is incorporated into the theory. Therefore, the film thickness dependence of ferroelectric and electro-optic properties in epitaxial BaTiO₃ thin films can be explained. Moreover, a large quadratic electro-optic effect was obtained in the BaTiO₃ thin films, which is in good agreement with the experimental result of BaTiO₃ thin films on the MgO substrate.