Topological Dirac surface states in ternary compounds GeBi2Te4, SnBi2Te4 and Sn0.571Bi2.286Se4

Using high-resolution angle-resolved and time-resolved photoemission spectroscopy, we have studied the low-energy band structures in occupied and unoccupied states of three ternary compounds GeBi₂Te₄, SnBi₂Te₄ and Sn_0.571Bi_2.286Se₄ near the Fermi level. In previously confirmed topological insulator GeBi₂Te₄ compounds, we confirmed the existence of the Dirac surface state and found that the bulk energy gap is much larger than that in the first-principles calculations. In SnBi₂Te₄ compounds, the Dirac surface state was observed, consistent with the first-principles calculations, indicating that it is a topological insulator. The experimental detected bulk gap is a little bit larger than that in calculations. In Sn_0.571Bi_2.286Se₄ compounds, our measurements suggest that this nonstoichiometric compound is a topological insulator although the stoichiometric SnBi₂Se₄ compound was proposed to be topological trivial.     

Time-resolved study of the lasing emission from high vibrational levels of N2^+ pumped with circularly polarized femtosecond pulses

We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses.This emission line corresponds to the B^2Σu^+(u'=4)-X^2Σg^+(u=3)transition of nitrogen ions.In the presence of an external seeding pulse,the 353.8 nm signal was amplified by 3 orders of magnitude.Thanks to the much enhanced intensity,we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique.It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure,while the radiation peak power grows up nearly quadratically with pressure,indicating that the 353.8 nm radiation is of the nature of superradiance.     

葡萄糖作钝化剂的绿光多晶薄膜钙钛矿发光二极管

金属卤化物钙钛矿发光二极管具有颜色可调、色纯度高、光谱稳定性好等优点,成为近年来的研究热点。溶液加工的多晶薄膜钙钛矿发光二极管制备工艺简单且成本低,但结晶过程中容易形成缺陷,进而影响器件性能。本文提出采用低成本的葡萄糖作为钝化剂,制备多晶薄膜钙钛矿发光二极管,葡萄糖的加入有效抑制了器件中缺陷诱导非辐射复合损失。在葡萄糖浓度为0.2 mol·L^-1时,缺陷钝化效果最佳,器件的最大亮度达到11 840 cd·m^-2,最大电流效率为7.89 cd·A^-1,光谱稳定性及色纯度好,且表现出较好的重复性。本文为多晶薄膜钙钛矿发光二极管中缺陷的钝化提供了简单而有效的方法。     

复合材料组分性能随机性识别的克里金随机分析方法

建立非均匀材料宏观力学性能与微结构参数之间的定量关系一直是人们所关心的问题,利用材料微结构参数和组分性能预报复合材料宏观力学性能,已经取得了很大的进展,然而已知复合材料宏观性能,如何开展组分性能的随机识别,目前的研究工作还不多见.论文考虑了复合材料的随机性,在已知复合材料宏观有效性能的随机性条件下,采用克里金随机分析方法,对复合材料组分性能的随机性进行识别,通过单向纤维复合材料的宏观有效性能的随机性,计算得到了纤维弹性模量的均值与方差,证明了该方法的有效性.     

非相干电离注入导致自由感应衰变信号的擦除效应（英文）

由强场中红外飞秒脉冲泵浦的氮离子能够以自由感应衰变（FID）的形式发出相干的前向辐射，该FID辐射可以被随后的800 nm飞秒脉冲有效抑制。这种擦除效应是对微弱FID辐射进行时间表征的独特工具，特别是在FID辐射与泵浦脉冲的谐波在频域重叠的情况下。基于密度矩阵与麦克斯韦方程的数值模拟结果，认为擦除效应主要是由于800 nm脉冲直接引发氮离子B态和A态相干性的变化，该变化进一步与800 nm脉冲耦合作用，引起了B态和X态之间相干性的减小，从而导致对应的391.4辐射的减弱。