Effect of Te doping on superconductivity and charge-density wave in dichalcogenides 2H-NbSe2-xTex （x = 0, 0.1, 0.2）

Single crystals of Te-doped dichalcogenides 2H-NbSe2-xTex （x ---- 0, 0.10, 0.20） were grown by vapour transport method. The effect of Te doping on the superconducting and charge-density wave （CDW） transitions has been investigated. The sharp decrease of residual resistance ratio, RRR = R（3OOK）/R（SK）, with increasing Te content was observed, indicating that the disorder in the conducting plane is induced by Te doping. Meanwhile the superconducting transition temperature, Tc, decreases monotonically with Te content. However, the CDW transition temperature, TCDW, shown by a small jump in the temperature dependence of the resistivity near 30 K, increases slightly. The results show that the suppression of superconductivity might be caused by the enhancement of CDW ordering. The disorder has little influence on the CDW ordering.     

乳化-前驱物热分解法制备纳米氧化锌

以 Zn(NO3 ) 2 · 6 H2 O、Na2 CO3 - Na HCO3 为原料 ,阴离子表面活性剂为乳化剂 ,有机溶剂为分散剂 ,采用乳化法制备前驱物 ,热分解前驱物得到纳米 Zn O;XRD物相分析表明 ,产物为标准六方晶系 ;Raman光谱表明产物是 Zn O晶体 ;并通过 TG- DTA确定前驱物分解成纳米 Zn O的最佳温度为 30 0℃。     

β型烧绿石氧化物超导体AOs2O6 (A=K, Rb) 的 声子软化与超导电性

运用基于密度泛函理论的第一性原理计算方法, 研究两种β 型烧绿石氧化物超导体AOs₂O₆(A=K, Rb) 的结构稳定性, 声子软化以及与超导电性的关系. 通过计算发现, AOs₂O₆中碱金属原子A(=K, Rb) 沿〈111〉 晶向具有不稳定性, 且以K原子的不稳定性更为突出. 同时, 计算得到的KOs₂O₆在布里渊区中心的声子频率普遍比RbOs₂O₆的低, 使得KOs₂O₆的电声子耦合常数比RbOs₂O₆的大. 本文计算结果表明, 较小的碱金属原子K位于较大的氧笼子中, 活动性较强, 导致声子的软化, 是引起KOs₂O₆具有较强的电声子耦合及较高的超导转变温度的根本原因. 这些结果对解释两种β 型烧绿石氧化物超导体AOs₂O₆(A=K, Rb) 的超导电性具有重要意义.     

The dynamics of hydrogen adsorption on polycrystalline uranium

The dynamics of dissociative hydrogen adsorption on clean polycrystalline uranium has been studied using temperature programmed desorption and supersonic molecular beams. The initial sticking probability was measured as a function of incident kinetic energy between 3 and 255 meV. Two adsorption channels were observed; a non-activated direct channel was shown to be active over the entire energy range studied and a low energy indirect channel that was characterised by a decrease in sticking probability with increasing beam energy, and an insensitivity to both surface temperature and a range of hydrogen coverages. Together these results suggest the existence of an unaccommodated molecular precursor that has sufficient lifetime and mobility to locate favourable sites and dissociatively adsorb.     

超声喷雾热解法制备SnS薄膜的物性研究

用超声喷雾热解法制备SnS多晶薄膜,对比了三种不同前驱液配比浓度对SnS薄膜性能的影响。XRD测试表明,当前驱液为硫脲(0.5 mol·L-1)+四氯化锡(0.5 mol·L-1)+去离子水时,SnO2的衍射峰强度比较大;当前驱液为硫脲(0.6 mol·L-1)+四氯化锡(0.5 mol·L-1)+去离子水时,SnS的衍射峰占主要地位,其中也含有一定量的SnO2;当前驱液为硫脲(0.7 mol·L-1)+四氯化锡(0.5 mol·L-1)+去离子水时,退火后的薄膜为单一的SnS薄膜,具有斜方晶系结构。SEM观测发现,薄膜均匀、致密,前驱液中硫脲浓度较大时,颗粒也较大。透过谱测试表明,浓度对薄膜透过率影响较小。结合器件的暗I-V和C-V测试,用三种前驱液配比浓度所制备的器件的结特性差异不大;当前驱液中硫脲浓度较大时,载流子浓度相对较大。     

Majorana费米子与拓扑量子计算

1937年,Majorana发现Dirac所提出的相对论性协变的电子波动方程,在另一个表象下所得到解可以描述不带电荷的费米子,具有与Dirac费米子不同的性质。在基本粒子领域,对这种Majorana费米子的寻找至今一直在进行中;而在凝聚态物理领域,对拓扑超导体和分数量子霍尔态的研究,人们已经发现了与Majorana费米子有相同行为的准粒子。特别是在二维拓扑超导体系中出现的涡旋元激发包含了零能量的Majorana准粒子,它们在交换操作下表现出非阿贝尔的统计性质,因而有望借以实现拓扑量子计算。文章系统地介绍了凝聚态物质系统中获得Majorana费米子的理论模型和物理实现,并进一步介绍了与之相关的拓扑量子计算的实现方法。     

非常规超导体及其物性

1986年高温铜氧化合物超导体的发现开辟了超导研究的新纪元,人们开始大量探索具有非常规超导机制的新型超导材料,以期发现具有更高超导转变温度的超导体。文章将结合作者多年来的研究,简要介绍具有代表性的非常规超导体材料家族及其物性,以及对非常规超导体材料研究的未来展望。     

Graphene/Mo_2C heterostructure directly grown by chemical vapor deposition

Graphene-based heterostructure is one of the most attractive topics in physics and material sciences due to its intriguing properties and applications. We report the one-step fabrication of a novel graphene/Mo_2C heterostructure by using chemical vapor deposition(CVD). The composition and structure of the heterostructure are characterized through energydispersive spectrometer, transmission electron microscope, and Raman spectrum. The growth rule analysis of the results shows the flow rate of methane is a main factor in preparing the graphene/Mo_2C heterostructure. A schematic diagram of the growth process is also established. Transport measurements are performed to study the superconductivity of the heterostructure which has potential applications in superconducting devices.     

铁基高温超导体电子结构的角分辨光电子能谱研究

铜氧化物超导体和铁基超导体是人类相继发现的两类高温超导家族,它们的高温超导机理是凝聚态物理领域中长期争论但悬而未决的重大问题.对铁基超导体广泛而深入的研究,以及与铜氧化物高温超导体的对比,对于发展新的量子固体理论、解决高温超导机理、探索新的超导体以及超导实际应用都具有重要意义.固体材料的宏观物性由其微观电子结构所决定,揭示高温超导材料的微观电子结构是理解高温超导电性的前提和基础.由于角分辨光电子能谱技术具有独特的同时对能量、动量甚至自旋的分辨能力,已成为探测材料微观电子结构的最直接、最有力的实验手段,在高温超导体的研究中发挥了重要作用.本文综述了在不同体系铁基超导体中费米面拓扑结构、超导能隙大小和对称性、轨道三维性和选择性、电子耦合模式等的揭示和发现,为甄别和提出铁基超导新理论、解决高温超导机理问题提供重要依据.     

Massless and quantized modes of kinks in the phase space of superconducting gaps

We investigated quantized modes of kinks in the phase space of superconducting gaps in a superconductor with multiple gaps. The kink is described by the sine-Gordon model in a two-gap superconductor and by the double sine-Gordon model in a three-gap superconductor. A fractional-flux vortex exists at the edge of the kink, and a fractional-flux vortex will be stable in a three-gap superconductor with time-reversal symmetry breaking. The kink and fractional-flux vortex exhibit massless modes as a sliding motion. We show further that there are one zero-energy mode (massless mode) and quantized excitation modes in kinks, which are characteristic features of multi-gap superconductors. The equation of quantized modes for the double sine-Gordon model is solved numerically. The correction to the ground-state energy is calculated based on the renormalization theory.