Universal Bottleneck for Thermal Relaxation in Disordered Metallic Films

JETP Letters - We study the heat relaxation in current biased metallic films in the regime of strong electron–phonon coupling. A thermal gradient in the direction normal to the film is...     

各向异性层状强关联金属中沿c轴方向的电荷输运

对于欠掺杂铜氧化物超导体 ,当温度Ｔ高于超导转变温度Ｔｃ 但低于赝能隙温度Ｔ 时 ,便有正常态赝能隙打开 (在ａｂ平面布里渊区的角隅位置 ) .赝能隙的存在对ｃ轴方向的电荷输运起阻碍作用 ,结果导致正常态输运行为的强二维性 ,即电阻率ρａｂ(Ｔ)的金属行为和 ρｃ(Ｔ)的绝缘体行为 .当温度降至Ｔｃ 以下 ,层间的约瑟夫森耦合使得材料转变为三维各向同性超导态 .其中有效维数的转变一直是凝聚态物理的一个热点课题 .上述维数转变的问题也存在于非超导的层状强关联金属中 ,例如 (Ｂｉ0 5Ｐｂ0 5) 2 Ｂａ3 Ｃｏ2 Ｏｙ(简称ＢＰＢ ＣＯ ,它…     

Effect of Nickel Distributions Embedded in Amorphous Carbon Films on Transport Properties

Electrical properties of C/Ni films are studied using four mosaic targets made of pure graphite and stripes of nickel with the surface areas of 1.78,3.21,3.92 and 4.64%.The conductivity data in the temperature range of400–500 K shows the extended state conduction.The conductivity data in the temperature range of 150–300 K shows the multi-phonon hopping conduction.The Berthelot-type conduction dominates in the temperature range of 50–150 K.The conductivity of the films in the temperature range about 50 K is described in terms of variable-range hopping conduction.In low temperatures,the localized density of state around Fermi level(F)for the film deposition with 3.92% nickel has a maximum value of about 56.2×10~(17)cm~(-3)eV~(-1) with the minimum average hopping distance of about 3.43 × 10~(-6) cm.     

Fredholm Determinants and the Statistics of Charge Transport

Using operator algebraic methods we show that the moment generating function of charge transport in a system with infinitely many non-interacting Fermions is given by a determinant of a certain operator in the one-particle Hilbert space. The formula is equivalent to a formula of Levitov and Lesovik in the finite dimensional case and may be viewed as its regularized form in general. Our result embodies two tenets often realized in mesoscopic physics, namely, that the transport properties are essentially independent of the length of the leads and of the depth of the Fermi sea.     

Absence of Transport Under a Slowly Varying Potential in Disordered Systems

In the tight-binding random Hamiltonian on Z ^d , we consider the charge transport induced by an electric potential which varies sufficiently slowly in time, and prove that it is almost surely equal to zero at high disorder. In order to compute the charge transport, we adopt the adiabatic approximation and prove a weak form of adiabatic theorem while there is no spectral gap at the Fermi energy.     

氧化石墨烯膜各向异性热传输特性研究

氧化石墨烯膜是一类新型的层状材料。本文报道了氧化石墨烯膜的面内和垂直于面方向的热扩散率和热导率,发现垂直于面方向的热导率比面内热导率低一个数量级,展示了明显的各向异性特征。氧化石墨烯膜的导热系数远低于单层石墨烯的导热系数,其原因主要是由于氧化石墨烯膜间的接触热租和氧化石墨烯膜本身导热系数较低造成的。     

Modified Potential Around a Moving Test Charge in Strongly Coupled Dusty Plasma

The theory of dynamical(wake) potential behind a moving test charge in a weakly coupled dusty plasma is extended to that including of strong interaction between dust grains. Such strong interaction is included in the dielectric response function by a generalized hydrodynamic(GH) fluid model. It is shown that the strong interaction between dusts including the lattice spacing correction has a significant effect on the wake potential in dusty plasma. This may be used to investigate basic features of phase transition and possibility of lattice formation of dusty plasma.     

锰掺杂近化学计量比铌酸锂晶体的电荷输运过程

用泵浦(350 nm)-探测(780 nm)法研究了轻度锰掺杂近化学计量比铌酸锂晶体的光致吸收的特征,结果表明光致吸收的暗衰减过程以扩展指数的形式衰减,并测量了饱和光致吸收、衰减时间常量和扩展因子对泵浦光光强的依赖关系.在z轴方向上加直流电场测量了紫外光照射下光伏打电流强度和光电导,发现它们与光强之间成超线性关系.实验结果可以用考虑本征缺陷能级和掺杂能级之间激发和复合的修正的双中心电荷输运模型进行定量的解释.     

Dimension Effects in Insulating NbTiN Disordered Films and the Asymptotic Freedom of Cooper Pairs

JETP Letters - We investigate the evolution of the electronic transport in disordered NbTiN films at the insulating side of the superconductor-insulator transition as function of the effective...     

Strongly Correlated Effect in TiS2

The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.     

掺杂PVK薄膜的荧光谱及电荷转移

根据PVK掺杂后荧光谱的变化，说明掺杂PVK薄膜的电致发光存在着从基质分子向掺杂分子的能量传递，用一个由单链模型扩展到包括杂质的哈密顿量进行数值求解，结果表明：在PVK和杂质分子之间有效的能量传递是源于它僮之间的电荷转移，且随着杂质浓度的变化，其荧光谱峰位的移动与掺杂前后系统总能量的改变及荧光谱强度与掺杂后转移的电荷数之间分别存在对应关系。该模型较好地解释了有关的实验结果。     

Suppression of Superconductivity in Disordered Films: Interplay of Two-Dimensional Diffusion and Three-Dimensional Ballistics

JETP Letters - Suppression of the critical temperature in homogeneously disordered superconducting films is a consequence of the disorder-induced enhancement of Coulomb repulsion. We demonstrate...     

A Study of the Spatial Charge Effect on 2-MeV Proton Beam Transport in an Accelerator-Based Epithermal Neutron Source

Technical Physics - A neutron source composed of a tandem accelerator with vacuum insulation and a lithium target is used to develop the boron neutron capture therapy and other applications. The...     

Memory Effects in Nonequilibrium Transport for Deterministic Hamiltonian Systems

We consider nonequilibrium transport in a simple chain of identical mechanical cells in which particles move around. In each cell, there is a rotating disc, with which these particles interact, and this is the only interaction in the model. It was shown in Ref. 1 that when the cells are weakly coupled, to a good approximation, the jump rates of particles and the energy-exchange rates from cell to cell follow linear profiles. Here, we refine that study by analyzing higher-order effects which are induced by the presence of external gradients for situations in which memory effects, typical of Hamiltonian dynamics, cannot be neglected. For the steady state we propose a set of balance equations for the particle number and energy in terms of the reflection probabilities of the cell and solve it phenomenologically. Using this approximate theory we explain how these asymmetries affect various aspects of heat and particle transport in systems of the general type described above and obtain in the infinite volume limit the deviation from the theory in Ref. 1 to first-order. We verify our assumptions with extensive numerical simulations.     

Current Neutralization and Charge Transport of an REB in Low-Pressure Argon

A numerical study of current neutralization and its effect on charge transport of a 0.175-MeV 6-kA 30-ns relativistic electron beam (REB) in argon at low pressure of 10-2-1 torr is presented. Contribution of two-stream instabilities to plasma conductivity is included in the calculations. The calculations show that energy coupled from beam to plasma is about 1-3 percent in the pressure range 0.1-1 torr. Though the two-stream contribution influences the time-dependent electron temperature and density around 0.1 torr, its effect on beam transport has been found to be only marginal. The results indicate that a maximum charge transport of 76 percent occurs around 0.08 torr when current neutralization is negligible. At 1-torr pressure, 75-percent current neutralization occurs and the charge transport is reduced to 40 percent. The numerical results have been compared with experiment and show good agreement in the pressure range 0.2-1 torr.     

Weak-Localization Effect on the Density of States in Disordered d-wave Superconductors

The weak-localization effect on the quasiparticle density of states (DOS) is studied with the diagrammatic technique in the binary-alloy model of disordered two-dimensional d-wave superconductors both in the Born and the unitary limits. We derive in details the expressions of the Goldstone modes (cooperon and diffuson) for quasiparticle diffuson. For generic Fermi surfaces, the DOS is shown to be subject to a quantum interference correction of logarithmic suppression. In the combined limit of unitarity and nested Fermi surface (the UN limit), it is found that the self-energy diagrams with two π-mode diffusons make additional contributions to the weak-localization effect, which has not been considered in the previous diagrammatic analysis. Due to the contributions of these new diagrams, the DOS in the UN limit is shown to have also a negative logarithmic correction, which is qualitatively different from the previous prediction.     

Annealing Effects on the Structural and Optical Properties of Thermally Deposited Tin Antimony Sulfide Thin Films

We report the deposition and characterization of tin antimony sulfide thin films on a soda glass substrate by a thermal evaporation technique. The thin films were annealed in argon gas at 150, 175, and 300 °C inside glass ampoules. The structural and optical properties of the deposited and annealed films are investigated. X-ray diffraction (XRD) patterns show that the films are polycrystalline in structure. Photoconductivity plot revealed good response in the NIR and visible regions, while the films show no transmittance below 700 nm. The absorption coefficient was of the order of 10⁶ cm^?1. Optical band gaps were also evaluated and a decrease in band gap was observed due to annealing. Hot point probe technique was employed for type of conductivity.     

Effective Charge in LiNbO3 Films Fabricated by Radio-Frequency Magnetron Sputtering Method

Physics of the Solid State - Amorphous Li–Nb–O films were deposited onto Si substrates by radio-frequency magnetron sputtering method. The fabricated heterostructures demonstrated the...