Topological Superconductivity in Cu(x)Bi(2)Se(3)

A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ～3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ～20 K and coexists with the topological superconducting state.     

Reactive chemical doping of the Bi2Se3 topological insulator

Using angular resolved photoemission spectroscopy we studied the evolution of the surface electronic structure of the topological insulator Bi(2)Se(3) as a function of water vapor exposure. We find that a surface reaction with water induces a band bending, which shifts the Dirac point deep into the occupied states and creates quantum well states with a strong Rashba-type splitting. The surface is thus not chemically inert, but the topological state remains protected. The band bending is traced back to Se abstraction, leaving positively charged vacancies at the surface. Because of the presence of water vapor, a similar effect takes place when Bi(2)Se(3) crystals are left in vacuum or cleaved in air, which likely explains the aging effect observed in the Bi(2)Se(3) band structure.     

Superconductivity in the doped topological insulator Cu{x}Bi{2}Se{3} under high pressure

We report a high-pressure single crystal study of the topological superconductor Cu{x}Bi{2}Se{3}. Resistivity measurements under pressure show superconductivity is depressed smoothly. At the same time the metallic behavior is gradually lost. The upper-critical field data B{c2}(T) under pressure collapse onto a universal curve. The absence of Pauli limiting and the comparison of B{c2}(T) to a polar-state function point to spin-triplet superconductivity, but an anisotropic spin-singlet state cannot be discarded completely.     

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.     

硼掺杂拓扑绝缘体Bi2Se3单晶的电输运性质研究

本文首次报道了用自助溶剂法(self-flux)制备优良的硼(B)掺杂硒化铋(Bi2BxSe3-x)样品的探索。实验结果显示掺杂样品中大部分B是以替代Se位方式存在,少量B以插入Bi2Se3晶格或范德瓦尔斯间隙的形式存在。当B的含量逐渐增加时,Bi2Se3的晶格常数c先减小后增加,且样品具有清晰的层状结构。掺杂量x=0.05的样品局部区域出现纳米带结构,同时该样品在低温下出现了明显的金属-绝缘转变现象。Bi2Se3样品电阻率随掺杂含量的增加而增加,表明B掺杂提高了样品表面态对整体电导的贡献,同时纳米带结构也有助于增加表面态的贡献。     

Electronic and magnetic reconstructions in La0.7Sr0.3MnO3/SrTiO3 heterostructures: a case of enhanced interlayer coupling controlled by the interface

We report on the magnetic coupling of La0.7Sr0.3MnO3 layers through SrTiO3 spacers in La0.7Sr0.3MnO3/SrTiO3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm.     

Improved multiferroic properties of La-doped 0.6BiFeO₃-0.4SrTiO₃ solid solution ceramics

The 0.6(Bi1-xLax)FeO 3-0.4SrTiO 3(x = 0,0.1) multiferroic ceramics are prepared by a modified Pechini method to study the effect of substitution of SrTiO3 and La in BiFeO3.The X-ray diffraction patterns confirm the single phase characteristics of all the compositions each with a rhombohedral structure.The magnetic properties of the ceramics are significantly improved by a solid solution with SrTiO3 and substitution of La.The values of the dielectric constant ε r and loss tangent tan δ of all the samples decrease with increasing frequency and become constant at room temperature.The La-doped 0.6BiFeO3-0.4SrTiO3 ceramics exhibit improved dielectric and ferroelectric properties,with higher dielectric constant enhanced remnant polarization(Pr) and lower leakage current at room temperature.Compared with a anti-ferromagnetic BiFeO3 compound,the 0.6(Bi0.9La0.1)FeO3-0.4SrTiO3 sample shows the optimal ferromagnetism with remnant magnetization M r ～ 0.135 emμ/g and ferroelectricity with Pr ～ 5.94 μC/cm 2 at room temperature.     

Observation of a warped helical spin texture in Bi2Se3 from circular dichroism angle-resolved photoemission spectroscopy

A differential coupling of topological surface states to left- versus right-circularly polarized light is the basis of many optospintronics applications of topological insulators. Here we report direct evidence of circular dichroism from the surface states of Bi(2)Se(3) using laser-based time-of-flight angle-resolved photoemission spectroscopy. By employing a novel sample rotational analysis, we resolve unusual modulations in the circular dichroism photoemission pattern as a function of both energy and momentum, which perfectly mimic the predicted but hitherto unobserved three-dimensional warped spin texture of the surface states. By developing a microscopic theory of photoemission from topological surface states, we show that this correlation is a natural consequence of spin-orbit coupling. These results suggest that our technique may be a powerful probe of the spin texture of spin-orbit coupled materials in general.     

新型层状Bi2Se3的第一性原理研究

近年来,在石墨烯研究热潮的推动下,众多种类丰富、性能各异的二维化合物材料相继被发现,其中一些二维材料具有多种同素异构体,进而呈现出更丰富的性质.层状Bi2Se3由于其独特的物理性质,受到人们广泛的关注,而它的同素异构体尚未有人研究.本文采用基于密度泛函理论的结构搜索方法,预测了一个稳定的b-Bi2Se3新相,它具有良好...     

Circular dichroism in core level photoemission from an adsorbed chiral molecule

The results of experimental measurements and theoretical simulations of circular dichroism in the angular dependence (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(110) are presented. Measurements in, and out of, substrate mirror planes distinguish CDAD due to the chirality of the sample and the experimental geometry. The effect due to sample chirality is relatively weak, so such measurements may not provide a routine spectral fingerprint of adsorbate chirality.     

Surface scattering via bulk continuum states in the 3D topological insulator Bi2Se3

We have performed scanning tunneling microscopy and differential tunneling conductance (dI/dV) mapping for the surface of the three-dimensional topological insulator Bi(2)Se(3). The fast Fourier transformation applied to the dI/dV image shows an electron interference pattern near Dirac node despite the general belief that the backscattering is well suppressed in the bulk energy gap region. The comparison of the present experimental result with theoretical surface and bulk band structures shows that the electron interference occurs through the scattering between the surface states near the Dirac node and the bulk continuum states.     

Photoemission study of YBa(2)Cu(3)O(y) thin films under light illumination

Heterojunctions of Nb-doped SrTiO3 substrate and YBa(2)Cu(3)O(y) thin films show photoconductivity and photovoltaic effects due to photocarrier injection. Photocarrier injection is expected to be a new carrier doping method in strongly correlated systems instead of chemical substitution. We have studied the nature of photocarrier injection in YBa(2)Cu(3)O(y)/SrTiO(3):Nb using x-ray photoemission spectroscopy with pulsed laser excitation. The core-level spectra shift to higher binding energy by 0.78 eV under pulsed laser illumination at 30 Hz. The energy shift corresponds to the photovoltage, which arises at the interface. In addition, we have observed that the energy shift strongly depends on the frequency of the laser. The lifetime of the injected photoholes has been estimated to be 40 ms by analyzing the frequency dependence.     

Spatial dependence of the dichroism of photoemission of Fe<Subscript>1/4</Subscript>TiTe<Subscript>2</Subscript> upon excitation with circularly polarized radiation

This paper reports on the results of the experimental investigation into the angular dependence of the photoemission of the valence band (the angle-resolved photoelectron spectrum) for the Fe_1/4TiTe₂ single crystal upon excitation with circularly polarized radiation. The angle-resolved photoelectron spectrum is studied in the vicinity of the Γ point of the Brillouin zone in the two directions ΓK and ΓM with the highest symmetry. The measurements are performed in noncoplanar geometry. The circular dichroism in the photoemission angular distribution is observed over the entire ranges of energies and angles. The magnitude of the dichroism depends on the choice of the band, the binding energy, and the polar angle and varies from 0 at the Γ point to 20%.     

High pressure transport properties of the topological insulator Bi2Se3

We report x-ray diffraction, electrical resistivity, and magnetoresistance measurements on Bi2Se3 under high pressure and low temperature conditions. Pressure induces profound changes in both the room temperature value of the electrical resistivity as well as the temperature dependence of the resistivity. Initially, pressure drives Bi2Se3 toward increasingly insulating behavior and then, at higher pressures, the sample appears to enter a fully metallic state coincident with a change in the crystal structure. Within the low pressure phase, Bi2Se3 exhibits an unusual field dependence of the transverse magnetoresistance Δρ(xx) that is positive at low fields and becomes negative at higher fields. Our results demonstrate that pressures below 8 GPa provide a non-chemical means to controllably reduce the bulk conductivity of Bi2Se3.     

Chiral orbital-angular momentum in the surface states of Bi2Se3

We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi2Se3. We observed circular dichroism (CD) as large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs in CD. The observed CD is attributed to the existence of local orbital-angular momentum (OAM). First-principles calculation shows that OAM in the surface states is significant and is locked to the electron momentum in the opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility for strong light-induced spin-polarized current in surface states. We also provide a proof for local OAM origin of the CD in ARPES.     

LaAlO3/SrTiO3界面的电子结构及光学性质的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,结合局域密度近似（LDA）研究了钙钛矿结构氧化物LaAlO3 /SrTiO3界面的电子结构及光学性质。能带结构分析表明当形成(AlO2)-/(TiO2)0界面时其禁带宽度为1.888 eV,呈现绝缘体的性质,当形成(LaO)+/(SrO)0界面时其禁带宽度为0.021 eV,呈现半导体或半金属性质。同时,对不同界面的光学性质也进行了研究,结果表明纯相的LaAlO3和SrTiO3的吸收系数、反射系数及能量损失谱强度明显高于由这两种单质形成不同界面的强度。     

Optical Spectroscopy of Kramers Doublets of an Er3+ Ion in a Two-Dimensional Frustrated Magnetic Cu3Er(SeO3)2O2Cl

Optics and Spectroscopy - Francisites, Cu3M(YO3)2O2X (M = Bi or rare earth, Y = Se, Te, X = Br, Cl, or I), attract close attention from researchers because of their interesting magnetic properties,...     

水热法制备表面修饰的钛酸锶纳米微粉

以工业原料和常用试剂ＴｉＣｌ４、Ｓｒ（）ＮＯ３）２和ＫＯＨ为基础原料，通过添加表面活性剂十二烷基苯磺酸（ＤＢＳ），并采用制备出表面包裹有ＤＢＳ的钛酸锶纳米微粉姘应用红外光谱，Ｘ射线衍射谱，透射电子显微镜，热分析等一系列手段对其微结构进行了表征。结果表明：样品为表面包裹ＤＢＳ的钛酸锶纳同粉，其形态较为规则，粒度分布较窄，单分散性较好，粒子的平均粒径为１２０ｍｍ，包裹膜的平均厚度为６ｎｍ左右，根据Ｘ光     

氢化物发生-原子荧光法直接测定锑及其化合物中的硒和铋

通过研究在不同酸度下Sb5+对Se,Bi的干扰情况,发现在高酸度下,Sb对Se,Bi的干扰明显减弱,并结合锑在不同价态发生氢化反应的差异性,建立了不需通过任何化学分离而直接测定锑及其相关产品中的微量硒和铋的方法,并用于实际样品的分析.方法对实际样品加标回收率在95%～105%之间,检测下限(含量)硒和铋分别为0.00004×10-2mg@L-1和0.0001×10-1mg@L-1,对实际样品分析精度分别为RSD(Se)=2.4%(含量为0.00169×10-2mg@L-1时),5.4%(含量为0.00056×10-mg@L-1时)和RSD(Bi)=5.0%(含量为0.00024×10-2mg@L-1时),1.3%(含量为0.00229×10-2mg@L-1时),完全满足实际样品分析的要求.     

Synthesis, Crystal Structure, DNA-binding Properties and Cytotoxic Activity of the Copper (II) Complex Involving Xanthone

1, 8-(3, 6, 9-Trioxaundecane-1, 11-diyldioxy)xanthone (L), and its new Cu (II) complex [Cu·L·(CH₃CN)₂](ClO₄)₂ have been synthesized and characterized by ¹H NMR, electrospray mass spectra (ESI-MS), elemental analyses, infrared spectra (IR) and X-ray single crystal diffraction. The crystal structure of complex shows that Cu (II) ion is encapsulated within the macrocycle of L. The geometry around copper is a distorted square bipyramid with two acetonitrile molecules at axial position, and four macrocyclic oxygens including the carbonyl oxygen on the equatorial positions. The interaction of Cu (II) complex with calf thymus DNA (ct DNA) has been investigated by spectrophotometric titrations, ethidium bromide (EB) displacement experiments, circular dichroism (CD) spectra and viscosity measurements. Rresults indicate that Cu (II) complex can intercalate into the DNA base pairs by the plane of xanthone ring. Furthermore, the Cu (II) complex was tested against tumor cell lines including ECA109, SGC7901and GLC-82 by MTT (microculture tetrazolium) method. The studies of DNA-binding agree with the effects on the inhibition of tumor cells in vitro.