Effect of Umklapp on the low temperature electrical resistivity of nonmagnetic dilute alloys

The deviation from Matthiessen's rule recently studied by Caplin and Rizzuto on Al based alloys is explained as an effect of the anisotropy of the Fermi surface on electon-phonon and electron-impurity scattering. Use is made of the diffusion theory of electrons by Klemens and Jackson.     

On the theory of the low-temperature electrical resistivity of potassium

Expressing the residual resistivity ?₀ as a force-force correlation, a first-principles basis is afforded for the low temperature expansion of the electrical resistivity ? as

(I)$\text{? = ?}{}_0\text{[1 +}\text{λ1}\text{λ}\text{+ … ]}$

where λ = const T^-2 is the non-resistive mean free path arising from electron-electron scattering. λ¹ is found to reflect directly long-range correlations in the electronic motions via the off-diagonal behaviour of the local density of states at the Fermi energy.     

Recovery of electrical resistivity in amorphous pdsi alloys after low temperature neutron irradiation

Measurements of electrical resistivity after low temperature fast neutron irradiation are made for amorphous Pd₈₀Si₂₀ and Pd₈₀Ni₂Sl₁₈ and then Pd₈₀Si₂₀ annealed at 230°C and 360°C, and the isochronal annealing curves are obtained. The resistivity increase of Pd₈₀Si₂₀ annealed at 360°C is about 10 times larger than that of amorphous alloys and no defined annealing stage is observed in amorphous alloys and Pd₈₀Si₂₀ annealed at 360°C. For amorphous Pd₈₀Si₂₀, about 60% of the resistivity increase by irradiation remains after annealing up to room temperature and these are discussed by the structural relaxation.     

First principles calculations of shock compressed fluid helium

The properties of hot dense helium at megabar pressures are studied with two first principles computer simulation techniques: path integral Monte Carlo simulation and density functional molecular dynamics. The simulations predict that the compressibility of helium is substantially increased by electronic excitations that are present in the hot fluid at thermodynamic equilibrium. A maximum compression ratio of 5.24(4)-fold the initial density was predicted for 360 GPa and 150,000 K. This result distinguishes helium from deuterium, for which simulations predicted a maximum compression ratio of 4.3(1). Hugoniot curves for statically precompressed samples are also discussed.     

The low temperature heat capacity and electrical resistivity of ReO3

Low temperature heat capacity and electrical resistivity measurements are reported for ReO₃. The heat capacity data give an acoustical mode Debye temperature θ = 327 K, and an electrronic density of states parameter γ = 2.83 mJ/mole-K². The observed temperature dependence of the resistivity is consistent with the existence of electron scattering both from acoustic mode phonons and from optical mode phonons of characteristic temperature θ_E = 1080 K. The above measurements are used to evaluate the electron-phonon interaction parameter λ = 0.24.     

固相硝基甲烷相变的第一性原理计算

研究极端条件下固相分子晶体含能材料的相变机理,对于人们认识固相含能材料的爆轰反应有着重要的意义.采用基于校正密度泛函理论的第一性原理方法研究固相硝基甲烷在静水压下的行为.分析晶格参数a,b和c轴随压强的变化,发现在1 GPa到12 GPa时晶格参数出现不连续的变化,表明体系发生相变.在相变时最大的二面角从155.3?增加到177.5?,二面角的增加限制CH3官能团自由旋转,使得C-N和C-H键的键长发生变化.在相变之前,体系主要存在由C-H···O组成的分子间的氢键,而在相变之后存在分子内的H···O和分子间C-H···O组成的氢键.此外通过对硝基甲烷体系的电子结构进行计算,发现相变会影响带隙随压强的变化,而且还会影响费米能级附近的态密度结构.     

The temperature dependence of the electrical resistivity of gold films

An analysis is presented of resistivity data on thin gold films with a view to characterizing any surface-caused quadratic temperature dependence (T²) to the resistivity. No evidence is found for a T² term varying in magnitude according to the inverse sample thickness. This is in accord with other studies on gold foils and disagrees with a recent suggestion that surface scattering causes a T² contribution to the resistivity of the noble metals.     

The temperature dependence of the electrical resistivity of granular metals

A simple percolation model of the hopping conduction in granular metals is proposed. The separation between the grains, in this model, is a random variable uncorrelated with the activation energy, the latter being dominated by the intragrain level splitting. The model is capable of reproducing the resistivity exp $\text{(}\text{T}{}_0\text{T}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ law over a wide temperature range, in spite of the narrow range of the grain diameters, explaining the recent observations of Choi et al.     

First principles calculations of cobalt doped zigzag graphene nanoribbons

We have investigated the stability and electronic properties of Co-doped zigzag graphene nanoribbons (ZGNR) by employing first principles calculations based on density functional theory. The results show that Co impurities settled in antiferromagnetic ground state which is ～2 meV favourable than ferromagnetic state. The formation energy indicates spontaneous formation of one-edge and centre doped structures, however, one-edge doping is found to be the most energetically favourable configuration. A charge transfer takes place from C to Co atoms which shows the formation of chemical bonding between C and Co. Binding energy also confirms the strong bonding of dopant Co impurity with C. The calculations show that band structures of all the ZGNR is substantially modified due to CoC charge transfer and the characteristic edge states of ZGNR are completely lost. Co-doping induces site independent enhanced metallicity irrespective of the ribbon widths. The broken degeneracy of electronic states in one-edge and centre doped ZGNR is important for spintronic applications.     

Superconducting transition temperature and low temperature resistivity in the niobium-hydrogen system

The impact-ionization rate in InSb at 300 K between 200 and 500 V/cm is found to beg(E)=210⁹ exp (–10³/E)s^–1 withE being the electric field (V/cm).We use current-voltage characteristics measured by A.C. Prior in 1957 [1]. In evaluating the impact-ionization rate we take into account Auger and linear recombination, surface generation,z-pinch compression, and doping of the sample. We also discuss the effects of ohmic heating and change in electron temperature. The rates evaluated from four independent measurements done by Prior agree reasonably well.     

V+注入锐钛矿TiO2第一性原理研究

用金属离子注入方法在锐钛矿TiO2薄膜中掺杂了V+,采用全势线性缀加平面波方法计算了锐钛矿TiO2及V+掺杂TiO2超原胞的电子结构,通过紫外-可见吸收光谱测试方法检测了注入不同剂量的V+对TiO2薄膜吸收光谱的影响.理论计算和实验结果表明,锐钛矿TiO2薄膜注入V+后,带隙宽度变小,吸收光谱发生红移,并且TiO2的带隙宽度随着注入V+剂量的增加而减小.     

The electrical resistivity of amorphous alloys at low temperatures

Measurements of the temperature- and magnetic field dependence of the electrical resistance of some metallic glasses are presented. The data obtained for Cu₅₇Zr₄₃, Cu₄₀Zr₆₀ and Pd₃₀Zr₇₀ demonstrate that deviations from the high temperature behaviour extrapolated to low temperatures are caused by superconducting effects. The paraconductivity which is strongly enhanced in amorphous alloys is shown to agree quite well with theoretical models. The normal state resistance does not saturate down to temperatures of about 2 K. It still exhibits a negative temperature coefficient of the resistivity.     

Low temperature electrical resistivity of α-cerium under pressure

We report a new method which is used to study the α-phase of cerium without inclusions of β-phase. A pressure independent low temperature resistivity has been observed. None of the exchange enhancement effects previously observed in high pressure susceptibility experiments have been detected on transport properties.     

Electron-electron interactions and the electrical resistivity of lithium at low temperatures

The electron-electron interactions in lithium metal have been examined keeping in view the recent developments. The contribution of the electron-electron Umklapp scattering processes in the electrical resistivity of lithium at low temperatures has been evaluated using a simplified spherical Fermi surface model with isotropic transition probability. Our values of the electrical resistivity so obtained compare fairly well with the experimental results for lithium.      

First principles calculations of Sr-based fluoroperovskite compounds under applied pressure

The structural, electronic and thermoelectric properties of SrXF₃ (X?=?Li, Na, K, Rb) compounds are performed using first principle calculations. The mBJ-GGA method has been considered to obtain accurate band gaps. The present compounds are found to be thermodynamically stable under 0?GPa and 10?GPa. This stability has been determined using the standard enthalypy of formation. The band structures of the compounds display direct band-gap (Γ-Γ). The band gap has slightly increased for almost studied compounds under 10?GPa. The Boltzmann transport calculations are used to calculate and explain the thermoelectric properties as a function of temperature within the range 20–1500?K. The majority charge carriers of SrXF₃ compounds are holes rather than electrons. Under 10 GP pressure the SrLiF₃ compound is shifted from n-type to p-type doping, whereas SrKF₃ and SrRbF₃ are shifted from p-type to n-type. SrNaF₃ has p-type doping character under 0?GPa and 10?GPa. The Seebeck coeffiecient is found to decrease, whereas σ/τ and S² σ/τ increase for higher temperature. According to the figure of merit and the high S² σ/τ values for SrXF₃, promising thermoelectric applications are expected for the present compounds.     

铝纳米晶的低温导电特性研究

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T~4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.