拓扑绝缘体(Bi0.5Sb0.5)2Te3薄膜中的线性磁阻

本文报道了拓扑绝缘体(Bi_0.5Sb_0.5)₂Te₃薄膜中线性磁阻问题的系统性研究工作. 此体系中, 线性磁阻在很宽的温度和磁场范围内出现: 磁场高达18 T时磁阻仍没有饱和趋势, 并且当温度不高于50 K时, 线性磁阻的大小对温度的变化不敏感. 栅压调控化学势可明显改变线性磁阻的大小. 当化学势接近狄拉克点时, 线性磁阻最为显著. 这些结果说明电荷分布的不均匀性是引起该材料线性磁阻的根源.     

Bi- and Au-Induced Reconstructions on GaAs（001）-2 × 4 Surface

Submonolayer Bi and Au adsorptions on the GaAs（001）-2× 4 surface are investigated by scanning tunnelling microscopy, low energy electron diffraction and first-principles calculations. The 1 ×4 and 3 × 4 reconstructed surface induced by Bi and Au, respectively, are revealed and their structural models are proposed based on experiments and first-principles calculations. Moreover, the validity of the recently proposed generalized electron counting （GEC） model [Phys. Rev. Lett. 97 （2006） 126103] is examined in detail by using the two surfaces. The GEC model perfectly explains the structural features, such Bi-1 × 4 surface and the 3x arrangement of four-atom Au as the characteristic short double-line structure in the clusters.     

Growth of Atomically Flat Ultra-Thin Ag Films on Si（111） by Introducing a √3×√3-Ga Buffer Layer

Growth of high-quality ultra-thin Ag film is of great interest from both scientific and technological viewpoints. First, ultra-thin metal fihns are model systems utilized to investigate quantum size effects （QSE）. When the film thickness is comparable to the Fermi wavelength of an electron, quantized energy lev- els known as quantum well states are produced in the surface normal direction. High-quality metal films with uniform thickness can effectively suppress in- homogeneous broadening of the thickness-dependent quantum levels to manifest quantum size effects. Secondly, Ag is the most widely used material for sur- face plasmonic devices, and high-quality Ag films have already shown the capability of supporting surface plasmon propagation fbr an extremely long distance. Moreover, ultra-thin Ag films can act as an excel- lent substrate for integrating various nano and low- dimensional structures. For instance, silicene, which is a two-dimensional （2D） sheet composed of silicon similar to graphene, has recently attracted intense attention. Ag （111） surface is widely recognized as the most important substrate suitable for the growth of silicene, while Ag films are much more cost-effective candidates for expensive single crystal Ag（111） sub- strates.     

硼烯的实验制备

硼烯作为目前发现的最轻的二维材料,表现出丰富的物理性质,包括高柔韧性、光学透明性、高热导率、近一维自由电子气、狄拉克费米子、超导电性等.然而,由于体相硼的层间共价键结合力较强,很难剥离出单层硼烯.另外,硼原子的缺电子属性,使其化学性质比较活泼,成键复杂,导致硼烯有很多同素异形体.长期以来,关于硼烯的研究停留在理论探索方面,硼烯的实验制备一直难以突破,直到最近几年才由少数课题组成功制备,至此关于硼烯的生长、结构以及电子性质研究打开了巨大的探索空间.本文主要从实验方向,系统综述了硼烯在不同衬底上的制备方法以及表现的不同结构相,并讨论了其生长机理.硼烯的制备为进一步扩展硼烯的物理性质提供研究平台,为探索硼烯的纳米器件制备提供思路,使得其在高能量储备、光电子器件、高检测灵敏度、柔性纳米器件等方面具有巨大的潜在应用前景.     

Na原子在Si(111)-(7×7)表面的吸附:从二维原子气到纳米团簇阵列

作者利用扫描隧道显微镜 (STM)详细研究了室温下Na原子在Si(111) (7× 7)表面的吸附 .对STM图像及功函数变化的分析表明 ,当Na原子覆盖度小于临界覆盖度 (0 .0 8ML)时 ,Na原子具有类气态的性质并可以在一个吸附能阱中快速移动 .从STM图像可看出这种移动导致的对比度调制 .在临界覆盖度以上 ,Na原子自组装形成团簇阵列 .第一原理模拟计算的结果与作者的实验结论很好吻合 .     

硅烯的化学功能化

硅烯是一种零能隙的狄拉克费米子材料,对其能带结构的有效调控进而打开带隙是硅烯进一步器件化的基础.而化学功能化是调控二维材料的结构和电子性质的一种有效方法.本文简要介绍了近几年在硅烯的化学功能化方面取得的进展,主要包括硅烯的氢化、氧化、氯化以及其他几种可能的化学修饰方法.     

Growth and transport properties of topological insulator Bi_2Se_3 thin film on a ferromagnetic insulating substrate

Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive investigation on the growth behaviors of prototype topological insulator Bi_2Se_3 thin film on a single-crystalline LaCoO_3 thin film on SrTiO_3 substrate, which is a strain-induced ferromagnetic insulator. Different from the growth on other substrates, the Bi_2Se_3 films with highest quality on LaCoO_3 favor a relatively low substrate temperature during growth. As a result, an inverse dependence of carrier mobility with the substrate temperature is found. Moreover, the magnetoresistance and coherence length of weak antilocalization also have a similar inverse dependence with the substrate temperature, as revealed by the magnetotransport measurements. Our experiments elucidate the special behaviors in Bi_2Se_3/LaCoO_3 heterostructures,which provide a good platform for exploring related novel quantum phenomena, and are inspiring for device applications.     

硅烯:一种新型的二维狄拉克电子材料

要硅烯是单原子层的硅薄膜,其结构与石墨烯类似,由于其奇特的物理性质特别是狄拉克—费米特性,在近年来引起了人们的关注。文章简要介绍了硅烯这一全新的二维体系在实验上的一些进展,包括实现硅烯在表面上的外延生长,重构的结构表征和相变,狄拉克电子特性的证实,以及可能具有的超导转变等。     

拓扑绝缘体薄膜生长与栅电压调控输运特性研究

文章讨论了三维拓扑绝缘体制备和输运性质研究方面的进展情况.首先介绍了拓扑绝缘体体材料和薄膜的制备,并介绍了文章作者利用分子束外延方法,在硅表面以及高介电常数材料钛酸锶表面生长高质量拓扑绝缘体Bi2Se3薄膜的工作.然后介绍了拓扑绝缘体输运研究的现状,以及文章作者在栅电压调控拓扑绝缘体外延薄膜的化学势和输运性质方面的研究成果.     

Observation of a Flat Band in Silicene

Flat bands that exhibit weak band dispersion in crystals can host heavy fermions that are cru- cial to many strongly correlated phenomena, such as ferromagnetism and superconductivity. For topologically trivial flat bands, theories have proven the stability of the ferromagnetic ground state i.e., flat band ferromagnetism. In the presence of weak disorders, systems with flat bands are expected to exhibit unconventional Anderson localization due to the lifting of degeneracy. More interestingly, flat bands with nontrivial topology, i.e., topological flat bands, are expected to host a fractional quantum Hall effect at zero magnetic field. Hence, searching for topologically trivial/nontrivial flat bands （TFB） has been an interesting while challenging task so far.