Anomalous Hall effect in polycrystalline Ni films

We systematically studied the anomalous Hall effect in a series of polycrystalline Ni films with thickness ranging from 4 to 200 nm. It is found that both the longitudinal and anomalous Hall resistivity increased greatly as film thickness decreased. This enhancement should be related to the surface scattering. In the ultrathin films (4–6 nm thick), weak localization corrections to anomalous Hall conductivity were studied. The granular model, taking into account the dominated intergranular tunneling, has been employed to explain this phenomenon, which can explain the weak dependence of anomalous Hall resistivity on longitudinal resistivity as well.     

Weak localization, hole-hole interactions, and the "Metal"-insulator transition in two dimensions

A detailed investigation of the metallic behavior in high-quality GaAs-AlGaAs two-dimensional hole systems reveals the presence of quantum corrections to the resistivity at low temperatures. Despite the low density ( r(s)>10) and high quality of these systems, both weak localization (observed via negative magnetoresistance) and weak hole-hole interactions (giving a correction to the Hall constant) are present in the so-called metallic phase where the resistivity decreases with decreasing temperature. If these quantum corrections persist down to T = 0, the results suggest that even at high r(s) there is no metallic phase in two dimensions.     

Transport Properties of Si and Ge Liquid Semiconductor Metals

In the present article, we study the electrical resistivity ρ, the thermoelectric power (TEP) α, thermal conductivity σ, Knight-Shifts and temperature coefficient of the Knight-Shifts of the liquid Si and Ge using the well known model potential for the first time. The structure factor used in the present work is derived from the Percus-Yevick (PY) theory. Various local field correction functions are used to study the screening influence. The present results of resistivity are found in qualitative agreement with available experimental and theoretical whenever exists.     

On the Planckian Limit for Inelastic Relaxation in Metals

JETP Letters - We consider the simplest model for temperature-linear growth of the resistivity in metals. It is shown that the so-called “Planckian” limit for the temperature dependent...     

Effect of Pressure on Heavy-Fermion Metals

In this paper, we introduce a microscopic theory for the heavy-fermion metals under applied pressure in the framework of the slave-boson mean-field approximation of the U = ∞ Anderson lattice model. The density of states for ƒ electrons and its variation with the pressure are calculated self-consistently The pressure-dependencies of the low-temperature specific-heat coefficient, magnetic susceptibility, and the resistivity in the electron-type and hole-type heavy-fermion metals are obtained. The results provide a unified explanation on the two opposite pressure-dependent effects observed in Ce-based and Yb-based compounds.     

μSR study of the S=1/2 triangular lattice antiferromagnet AgNiO2

AgNiO₂, a model compound of an S=1/2 triangular lattice, was studied by muon spin relaxation in addition to ac, dc susceptibility, electrical resistivity and neutron diffraction. The relaxation rate shows a sharp peak at around T_N=28 K followed by a sudden decrease of initial asymmetry indicating a magnetic ordering. Three internal fields ranging from 0.2 to 0.3 T were obtained from the muon precession period. However, a neutron diffraction experiment failed to detect any magnetic order at low temperatures. From these results, it was concluded that magnetic coherence is confined to small domain compared with the coherence length of neutron diffraction due to spin frustration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Balance Equation Approach to Nonlinear Polaronic Transport

Balance equations beyond the lowest order perturbation expansion for high-field electronic transport are developed and used to discuss the polaronic resistivity in polar semiconductors and other systems. Significant corrections in the case of high electric field are expected.     

TC2 dynamics and top quark production at NLC

We calculate the correction of the TC2 dynamics to the production cross section of the process in the top color-assisted multiscale technicolor model. Our results show that the corrections mainly come from the effects of the top color gauge boson in the s-channel. The total corrections to cross sections and are very large; this can be detected at NLC. The total corrections to the polarized parameters and may be observed at NLC in most of the parameter space. Received: 4 September 1999 / Revised version: 19 November 1999 / Published online: 17 March 2000     

Small mass enhancement near the metal–insulator transition in gated silicon inversion layers

The strong resistivity changes in the metallic state of two-dimensional electron systems have recently been assigned to quantum interaction corrections in the ballistic regime. We have performed analysis of Shubnikov–de Haas oscillations on high-mobility silicon inversion layers where we have explicitly taken into account that the back scattering angle has different influence on momentum relaxation and quantum life time. The consistent analysis under the assumption of the ballistic interaction corrections leads to smaller increase of the effective mass with decreasing electron density as usually reported.     

Magnetogravitational Stability of Resistive Plasma through Porous Medium with Thermal Conduction and FLR Corrections

The problem of stability of self gravitating magnetized plasma in porous medium is studied incorporating electrical resistivity, thermal conduction and FLR corrections. Normal mode analysis is applied to derive the dispersion relation. Wave propagation is discussed for parallel and perpendicular directions to the magnetic field. Applying Routh Hurwitz Criterion the stability of the medium is discussed and it is found that Jeans' criterion determines the stability of the medium. Magnetic field, porosity and resistivity of the medium have no effect on Jeans' Criterion in longitudinal direction. For perpendicular direction, in case of resistive medium Jeans' expression remains unaffected by magnetic field but for perfectly conducting medium magnetic field modifies the Jeans' expression to show the stabilizing effect. Thermal conducitivity affects the sonic mode by making the process isothermal instead of adiabatic. Porosity of the medium is effective only in case of perpendicular direction to magnetic field for perfectly conducting plasma as it reduces the stabilizing effect of magnetic field. For longitudinal wave propagation, though FLR corrections have no effect on sonic mode but it changes the growth rate for Alfvén mode. For transverse wave propagation FLR corrections and porosity affect the Jeans' expression in case of nonviscous medium but viscosity of the medium removes the effect of FLR and porosity on Jeans' condition.     

High pressure behaviour of liquid caesium

This paper deals with the anomalous behaviour of liquid caesium at high pressures. A model for the phenomenon of electron collapse in the liquid phase, based on the anomalous density variation of liquid caesium with pressure has been proposed. The process of 6s→5d electron collapse is pictured as the formation of a virtual bound state and the tunnelling process accounts for the 6s⇌5d dynamic conversion. The same model together with the Friedel sum rule has been used to explain the resistivity variation of liquid caesium with pressure. The resistivity minimum observed in most of the liquid alkali metals in the low pressure region has been explained. The agreement with the experimental curve is good in the low pressure region whereas a large discrepancy exists at higher pressures. This may be due to the breakdown of the Ziman’s resistivity formula under conditions of resonance scattering.     

Weak localization corrections to the anomalous Hall effect

We calculate localization corrections to the anomalous Hall conductivity in the framework of side-jump and skew scattering mechanisms. In contrast to the ordinary Hall effect, there exists a nonvanishing localization correction to the anomalous Hall resistivity. The correction to the anomalous Hall conductivity vanishes in case of side-jump mechanism, but is nonzero for the skew scattering.     

铁磁金属中自旋波散射引起的电阻率

铁磁金属中自旋向上电子与自旋向下电子的能量由于磁化而造成的分裂,在低温下对自旋波散射引起的电阻率(磁电阻率)有重要的影响。由于这个分裂,单带情况下低温磁电阻率总是衰减的;但两带情况下则有可能增强。考虑到自旋波谱中的能隙用单带模型所得的磁电阻率表达式与Tb和Dy的实验资料比较表明:不但低温电阻率的温度依赖性符合,数值上也与高温磁电阻测量结果一致。 关键词：     

Measurement of the bulk acoustic properties of fibrous materials at high temperatures

It is common for fibrous porous materials to be used in high temperature applications such as automotive and gas turbine exhaust silencers. Understanding the effect of temperature on the acoustic properties of these materials is crucial when attempting to predict silencer performance. This requires knowledge of the bulk acoustic properties of the porous materials and so this article aims to quantify the effect of temperature on the bulk acoustic properties of three fibrous materials: rock wool, basalt wool and an E-glass fibre. Measurements are undertaken here using a standard impedance tube that has been modified to accommodate temperatures of up to 500 °C. It is shown that measured data for the bulk acoustic properties may be collapsed using a standard Delany and Bazley curve fitting methodology provided one modifies the properties of the material flow resistivity and air to account for a change in temperature. Moreover, by using a previously proposed power law describing the dependence of the flow resistivity with temperature, one may successfully collapse data measured at every temperature and obtain the Delany and Bazley coefficients in the usual way. Accordingly, to predict the bulk acoustic properties of a fibrous material at elevated temperatures it is necessary only to measure these properties at room temperature, and then to apply the appropriate temperature corrections to the properties of the material flow resistivity and air when using the Delany and Bazley formulae.     

Leading Electroweak Corrections to the Neutral Higgs Boson Production at the Fermilab Tevatron

We calculate the leading electroweak corrections to the light neutral Higgs boson production via qq → WH at the Fermilab Tevatron in both the standard model and the minimal supersymmetric model, which arise from the top-quark and Higgs boson loop diagrams. We found that the leading electroweak corrections can exceed the QCD corrections for favorable values of the parameters in the MSSM, but such corrections are only about -2%~-4% in the SM, which are much smaller than the QCD corrections. For the mass region of 90 < mh, < 120 GeV, the leading electroweak corrections can reach -20% for large tan β, and these corrections may be observable at a high luminosity Tevatron; at the least, new constraints on the tan β can be established.     

Universally coupled extraZ bosons from extended technicolor models

We show that in extended technicolor models there are several neutralZ bosons whose couplings to fermions are independent of family. TheseZ bosons are therefore additional to that of the standard model and induce corrections to the low energy effective Hamiltonian. These corrections are calculated in the most general model which includes technileptons (introduced to give mass to leptons).     

Negative magnetoresistance and hall coefficient of a two-dimensional disordered system

Localization corrections to the longitudinal (δρ) and Hall (δρ_H) resistivities of a two-dimensional disordered system are calculated in all ranges of classical magnetic fields, up to the values at which the mean free path of charge carriers l is less than or of the order of the cyclotron radius R _c. It is shown that the physical reason for the departure of the l dependence of these resistivities from the logarithmic law ∝ ln(l _B /l)) (l _B is the magnetic length) at is the nonlocal process of diffusion in the Cooper channel, rather than the transition to a quasi-ballistic regime. Analytical expressions are obtained that allow one to analyze the interference effect in δρ and δρ_H in quantizing magnetic fields , including the quantum limit. Contrary to popular opinion, the localization corrections to ρ_H are shown to be nonzero. They have a sign opposite to that of the charge carriers and lead to a decrease in the magnitude of the Hall resistivity. Their field dependence has the same features and their relative magnitude is of the same order as in the case of the longitudinal resistivity. The quantum corrections to the Hall resistivity are due to the Larmor precession of the closed paths that electrons follow in the process of their multiple scattering by randomly distributed impurities.     

纯金属电阻率的统计模型

本文提出了纯金属电阻率与声子浓度及声子平均动量的平方成正比的统计模型，由此简化模型，给出了纯金属电阻率的一个解析表达式，理论与实验规律相符，即在高温时，电阻率与温度Ｔ成正比，低温时与Ｔ＾５成正比。     

Top pair production in the littlest Higgs model with T-parity

In the framework of the littlest Higgs model with T-parity,we study the top pair production at the next generation colliders like LHC and ILC.We find that the order O(αs) corrections to the standard model top pair production cross section at LHC can be very small and the magnitude is below 1%.However,the magnitude of corrections to the standard model top pair production rate at ILC may be over 5% for reasonable values'of the parameters.Besides this,the corrections to the asymmetry ALR(tt) may be more sizable. Therefore,the top pair production at ILC may serve as a probe of the littlest Higgs model with T-parity,especially the asymmetry ALR(tt).     

Theoretical approach to microwave-radiation-induced zero-resistance states in 2D electron systems

We present a theoretical model in which the existence of radiation-induced zero-resistance states is analyzed. An exact solution for the harmonic oscillator wave function in the presence of radiation, and a perturbation treatment for elastic scattering due to randomly distributed charged impurities, form the foundations of our model. Following this model most experimental results are reproduced, including the formation of resistivity oscillations, their dependence on the intensity and frequency of the radiation, temperature effects, and the locations of the resistivity minima. The existence of zero-resistance states is thus explained in terms of the interplay of the electron microwave-driven orbit dynamics and the Pauli exclusion principle.