Electronic specific heat of nanographite ribbons

The electronic specific heat of nanographite ribbons exhibits rich temperature dependence, mainly owing to the special band structures. The thermal property strongly depends on the geometric structures, the edge structure and the width. There is a simple relation between the ribbon width and the electronic specific heat for the metallic or semiconducting armchair ribbons. However, it is absent for the zigzag ribbons. The metallic armchair ribbons exhibit linear temperature dependence. The semiconducting armchair ribbons exhibit composite behavior of power and exponential functions. As for the zigzag ribbons, the temperature dependence of the specific heat is proportional to T^1−p. The value of p quickly increases from to 1 as the ribbon width gradually grows. The zigzag ribbons might be the first system which exhibits the novel temperature dependence. The nanographite ribbons differ from an infinite graphite sheet, which illustrates that the finite-size effects are significant.     

Electronic specific heat for the Anderson model

The expression of the electronic specific heat for the symmetric Anderson model is obtained in closed form.     

Electronic specific heat of gamma phase copper-aluminum alloys

The electronic specific heat of the γ₂- and δ-phases in the binary copper-aluminum system has been measured as a function of composition. A pronounced minimum is observed in the corresponding variation in the density-of-states at the Fermi level with electron/atom ratio. This supports the view that the electronic structure is determined by contact between the Fermi surface and the relevant Jones zone for the γ₂-phase and that zone overlap effects are significant for higher electron concentrations. The data for the δ-phase strongly suggest that its electronic structure is very similar to that of the γ₂-phase. Recent transport measurements on copper-aluminum alloys are interpreted in terms of the present results.     

Electronic spectroscopy of Se2- in KBr

Rapid quenching of KBr crystals doped with Se^2- gives isolated Se^2- ions which are strongly luminescent. Two emission spectra were observed, one with a maximum intensity at about 14100 cm^-1 and the other with a maximum intensity at about 17200 cm^-1. Only the red emission is observed by excitation into the lowest energy absorption band at 24600 cm^-1, while between 10 K and about 150 K both red and yellow emissions are observed by excitation into the second absorption band at 26770 cm^-1. Both are assigned to the isolated Se^2- center in different distorted charge transfer states. The yellow emission is observed below about 100 K, reaches maximum intensity at about 35 K and is absent below 10 K. There are complementary changes in the intensity of the red emission so that the sum of the two emission intensities is constant. The absorption spectra of the isolated Se^2- and the (Se^2--vacancy) pair have been identified as well as the spectrum of a cluster of two or more (Se^2--vacancy) pairs.     

The specific heat of CeAl2 between 0.02 and 1 K

We report specific heat measurements on a CeAl₂ single crystal between 0.02 and 1 K. Above 0.08 K, we found C₀ = γT + βT³ with γ = (130±0.5) mJ/K²mole and β = (142±1) mJ/K⁴mole in good agreement with previous results above 0.3 K. Below 0.08 K, an excess specific heat C_N = αT^?2 with α = (6.4±1) mJK/mole was detected and interpreted in terms of hyperfine splitting of the Al²⁷ nuclear states. Our results suggest that in CeAl₂ (complex) antiferromagnetism coexists with the Kondo effect at least down to 20 mK.     

若干In2Se3化合物的晶体结构与电子特性

In_2Se_3是一种常见的A_2~ⅢB_3~Ⅵ型半导体,在不同温度下可表现出不同的物相,对应的晶格参数与物理性质也会有所不同.在过去几十年间,In_2Se_3的多相性引起了人们的关注,各物相的晶体结构被广泛地研究.近年来,研究发现α-In_2Se_3具有优异的光电、压电性能以及独特的铁电性能,可以预见它将在未来的半导体电子器件中发挥出重要的作用.本文综述了一系列In_2Se_3化合物的晶体结构与电子特性,我们首先简要介绍了这些In_2Se_3化合物的基本知识,接着详细讨论了它们的晶体结构与电子特性,最后对In_2Se_3化合物的研究前景进行了展望.     

若干In2Se3 化合物的晶体结构与电子特性

等离激元是金属中自由电子的集体振荡,其在物理,生物、化学、能源、信息等领域具有重要的应用前景。近些年来对等离激元量子效应研究的深入开展使得等离激元研究迈入了新阶段。本文首先简要介绍了等离激元的两个基本特性：光压缩效应和局域电场增强效应;随后回顾了量子等离激元方面的最新的进展,包括量子纠缠效应,量子尺寸效应,量子遂穿效应,等离激元在台阶势垒处的反射与激发,等离激元对电子相干效应的增强;最后对量子等离激元研究进行了总结和展望。     

Electronic and optical properties of defect chalcopyrite HgAl2Se4

The structural, electronic and optical properties of HgAl₂Se₄ are investigated using the full potential linear augmented plane wave method based on density functional theory. The calculated structural parameters using LDA are in excellent agreement with the available experimental result. The obtained energy band gap (2.24 eV) using EV-GGA approximation is in excellent agreement with experimental data (2.20 eV). Variation in the energy band gap as a function of the unit cell lattice parameter has been studied. The optical properties show a considerable anisotropy, which makes this compound very useful for various linear–nonlinear optical devices.     

Electronic and optical properties of layered chalcogenide FeIn2Se4

We investigated the spectral-dependent dielectric function and temperature-dependent bandgap energy of layered chalcogenide FeIn₂Se₄ crystals. The critical-point energy and Lorentzian broadening were analyzed by fitting second-derivative spectra using the standard critical point model. The temperature effect of the bandgap energy was analyzed based on an analytical model considering both thermal lattice expansion and electron–phonon interactions. We also extensively analyzed the temperature dependence of absorption tails and identified their possible origins. The dielectric functions and absorption coefficient in the photon-energy range of 0.75–4.75 eV were obtained. The results also showed that optical phonon modes associated with the electron–phonon interactions could be closely related to the average phonon energy.     

Low-temperature specific heat of TlCrS2

The specific heat of the ferromagnetic semiconductor TlCrS₂ is investigated experimentally, and the thermodynamic parameters are calculated. It is demonstrated that the temperature dependence of the magnetic specific heat of the TlCrS₂ compound is characteristic of quasi-two-dimensional magnetic systems.     

Carrier transport in Bi2Se3 topological insulator slab

Electron transport in Bi₂Se₃ topological insulator slabs is investigated in the thermal activation regime (>50 K) both in the absence (ballistic) and presence of weak and strong acoustic phonon scattering using the non-equilibrium Green function approach. Resistance of the slab is simulated as a function of temperature for a range of slab thicknesses and effective doping in order to gain a handle on how various factors interact and compete to determine the overall resistance of the slab. If the Bi₂Se₃ slab is biased at the Dirac point, resistance is found to display an insulating trend even for strong electron–phonon coupling strength. However, when the Fermi-level lies close to the bulk conduction band (heavy electron doping), phonon scattering can dominate and result in a metallic behavior, although the insulating trend is retained in the limit of ballistic transport. Depending on values of the operating parameters, the temperature dependence of the slab is found to exhibit a remarkably complex behavior, which ranges from insulating to metallic, and includes cases where the resistance exhibits a local maximum, much like the contradictory behaviors seen experimentally in various experiments.     

Closed tube sublimation growth of Ga2Se2: Solid-vapour equilibria and mass transport2

A detailed study of the real conditions of Ga₂Se₂ growth by sublimation in a closed tube system is presented. Mass flow measurements have been carried out as a function of the cross-section of the silica tubes, the thermal gradient along the growth chamber, and the sublimation temperature. With the aid of the results of pressure measurements, flow rates as a function of growth parameters have been evaluated according to diffusion theory, and compared with experimental flow rates. Useful information about the thermodynamic functions ΔH and ΔS of Ga₂Se₂ has thus been obtained.     

The low temperature specific heat of NpOs2 and NpRu2

Specific heat measurements on NpOs₂ show a peak at T_c = 7.9 ± 0.1 K, and γ = 90 mJ/(mol K²) above T_c. The magnetic entropy, 0.2 R 1n 2, supports previous arguments for itinerant ferromagnetism. The data for NpRu₂, supposedly a spin fluctuation compound, are fit below 10 K by C/T = γ + BT², with γ = 118 mJ/(mol K²) and B corresponding to θ_D = 174 K.