Density fluctuation spectrum in whistler turbulence

We develop a nonlinear two-dimensional fluid model of whistler turbulence that includes effect of electron fluid density perturbations. The latter is coupled nonlinearly with wave magnetic field. This coupling leads essentially to finite compressibility effects in whistler turbulence model. We find from our simulations that despite strong compressibility effects, the density fluctuations follow the evolution of the wave magnetic field fluctuations. In a characteristic regime where large scale whistlers are predominant, the coupled density fluctuations are found to follow a Kolmogorov-like phenomenology in the inertial range turbulence. Consequently, the turbulent energy is dominated by the large scale (compared to electron inertial length) eddies and it follows a Kolmogorov-like k−7/3 spectrum, where k is a characteristic wavenumber.     

Finite Larmor radius effect on thermal instability of a compressible plasma

The thermal instability of a compressible plasma in the presence of a uniform vertical magnetic field is studied to include the effects of finiteness of the ion Larmor radius. When the instability sets in as stationary convection, both the compressibility and the finite Larmor radius are found to have stabilizing effect. The sufficient conditions for the nonexistence of overstability are investigated.     

Compressibility measurements of quasi-one-dimensional quantum wires

We report measurements of the compressibility of a one-dimensional quantum wire, defined in the upper well of a GaAs/AlGaAs double quantum well heterostructure. A wire defined simultaneously in the lower well probes the ability of the upper wire to screen the electric field from a biased surface gate. The technique is sensitive enough to resolve spin splitting of the subbands in the presence of an in-plane magnetic field. We measure a compressibility signal due to the 0.7 structure and study its evolution with increasing temperature and magnetic field. We see no evidence of the formation of the quasibound state predicted by the Kondo model, instead our data are consistent with theories which predict that the 0.7 structure arises as a result of spontaneous spin polarization.     

Geodesic plasma compressibility effects on the magnetic islands in a tokamak

It is shown that the stability of rotating magnetic islands in a tokamak plasma is affected by plasma compressibility related to the geodesic curvature in an inhomogeneous magnetic field. A robust contribution has been found to the Rutherford evolution equation. It is shown that the sign of the geodesic curvature contribution is opposite to the sign of the polarization term. It is suggested that this mechanism plays a crucial role in the stability of small scale magnetic islands.     

Hysteresis in small arrays of interacting magnetic nanoparticles

The out-of-plane hysteresis loops of small arrays of magnetic nanoparticles, under the influence of an external field applied perpendicular to the array and the dipolar interaction are investigated. The particles are assumed to have a perpendicular anisotropy energy that tends to align the magnetic moments to be perpendicular to the array. The magnetization is found to exhibit a plateaux-and-jumps structure as the external field is swept up and down. These jumps are associated with jumps in the energy of the system, and correspond to transition from one configuration of the moment orientation to another. The energy of different configurations of the magnetic moments for a 3×3 array in the limit of weak dipolar interaction is analyzed, as a means to understand the hysteresis loop. These jumps are more pronounced in arrays of smaller sizes and when the dipolar interaction is weak. The configuration of magnetic moments at zero external field as the field is swept up and down is found to be highly sensitive to the dipolar interaction.     

Compressibility of a two-dimensional electron gas in a parallel magnetic field

The thermodynamic compressibility of a two-dimensional electron system in the presence of an in-plane magnetic field is calculated. We use accurate correlation energy results from quantum Monte Carlo simulations to construct the ground state energy and obtain the critical magnetic field B_c required to fully spin polarize the system. Inverse compressibility as a function of density shows a kink-like behavior in the presence of an applied magnetic field, which can be identified as B_c. Our calculations suggest an alternative approach to transport measurements of determining full spin polarization.     

磁介质力、热、磁混合效应的热力学描述

采用热力学方法讨论了顺磁介质系统的力、热、磁直接效应以及它们之间的交叉效应,得到了磁化率与压缩系数、热容量与压缩系数间的关系,并讨论了力磁效应的二级近似行为．     

Finite Larmor radius and Hall effects on thermal instability of a compressible plasma

The effects of compressibility, finite Larmor radius (FLR) and Hall currents are considered on the thermal instability of a plasma in the presence of a uniform horizontal magnetic field. For stationary convection, the compressibility has a stabilizing effect whereas FLR and Hall currents have stabilizing as well as destabilizing effects. For (C _pβ/g)<1, the system is stable. The magnetic field, FLR and Hall currents introduce oscillatory modes in the system for (C _pβ/g)>1.     

Reflectivity and microwave absorption in crystals with alternating intrinsic Josephson junctions

We compute the frequency and magnetic field dependencies of the reflectivity R(omega) in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c axis. The parameter alpha describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa1-xSr xCuO (4-delta) superconductor from two independent optical measurements, the fit of the loss function L(omega) at zero magnetic field and the magnetic field dependence of the peak positions in L(omega). The experiments are consistent with a free electron value for alpha.     

Two-dimensional Monte Carlo simulations of structures of a suspension comprised of magnetic and nonmagnetic particles in uniform magnetic fields

The structures of suspensions comprised of magnetic and nonmagnetic particles in magnetic fields are studied using two-dimensional Monte Carlo simulations. The magnetic interaction among magnetic particles, magnetic field strength, and concentrations of both magnetic and nonmagnetic particles are considered as key influencing factors in the present work. The results show that chain-like clusters of magnetic particles are formed along the field direction. The size of the clusters increases with increasing magnetic interaction between magnetic particles, while it keeps nearly unchanged as the field strength increases. As the concentration of magnetic particles increases, both the number and size of the clusters increase. Moreover, nonmagnetic particles are found to hinder the migration of magnetic ones. As the concentration of nonmagnetic particles increases, the hindrance on migration of magnetic particles is enhanced.     

Magnetic field and symmetry effects in small quantum dots

Shell phenomena in small quantum dots with a few electrons under a perpendicular magnetic field are discussed within a simple model. It is shown that various kinds of shell structures, which occur at specific values for the magnetic field lead to a disappearance of the orbital magnetization for particular magic numbers for noninteracting electrons in small quantum dots. Including the Coulomb interaction between two electrons, we found that the magnetic field gives rise to dynamical symmetries of a three-dimensional axially symmetric two-electron quantum dot with a parabolic confinement. These symmetries manifest themselves as near-degeneracy in the quantum spectrum at specific values of the magnetic field and are robust at any strength of the electron-electron interaction. A remarkable agreement between experimental data and calculations exhibits the important role of the thickness for the two-electron quantum dot for analysis of ground state transitions in a perpendicular magnetic field. The text was submitted by the author in English.     

An exact solution of the relativistic equation of motion of acharged particle driven by a circularly polarized electromagnetic waveand a constant magnetic field

An exact solution is found for the relativistic equation of motion of a charged particle driven by a circularly polarized electromagnetic wave and a constant magnetic field. The explicit expressions of particle position and velocity are obtained for certain initial conditions. The results are of interest to the interaction of the high-power laser with the magnetized plasma, electromagnetically pumped free-electron laser with a guide magnetic field, propagation of electromagnetic wave signals through a re-entry plasma sheath in the presence of a strong magnetic field, and magnetic confinement plasmas     

二维极化子在磁场中的基态能量

谐振子算符的代数运算方法被用于研究磁场中同时与表面光学声子及表面声学声子相互作用的二维电子。得到二维极化子在强磁场中直至四级微扰的基态能量以及它在任意强经磁场中的二级微扰基态能量表达式。结果发现,对磁场中二维极化子基态能量的影响中,表面声学声子有着与表面光学声子同样的甚至更为突出的贡献,是不容忽视的。 关键词：     

Lamellar-like structures in ferrofluids placed in strong magnetic fields

We consider a ferrofluid system consisting of magnetic particles interacting with a magnetic dipole–dipole interaction. We study the strong magnetic field regime where all magnetic dipoles are completely polarized in the direction of the magnetic field. We introduce a lattice gas model that serves to describe space ordering phenomena in such systems. It is found that, within mean field theory, this model predicts a second order phase transition to a phase with inhomogeneous lamellar-like ordering below a certain critical temperature.     

Thermodynamic signature of a two-dimensional metal-insulator transition

We present a study of the compressibility kappa of a two-dimensional hole system which exhibits a metal-insulator phase transition at zero magnetic field. It has been observed that dkappa/dp changes sign at the critical density for the metal-insulator transition. Measurements also indicate that the insulating phase is incompressible for all values of B. Finally, we show how the phase transition evolves as the magnetic field is varied and construct a phase diagram in the density-magnetic field plane for this system.     

Diamagnetic domains and magnetostriction in beryllium

Magnetostriction was for the first time studied under the conditions of formation of diamagnetic domains (Condon domains). Transverse magnetostriction oscillations on a beryllium single crystalline plate oriented normally to magnetic field were measured in magnetic fields up to 7 T at temperatures down to 1.5 K. The relative amplitude of oscillations increased almost as the square of magnetic field and reached 10^?5. The signal had a sawtoothed shape corresponding to alternation of homogeneous and inhomogeneous (domain) states in the region of the existence of magnetic domains. The arising of domains was accompanied by singularities in the observed signals which is explained by an anomalous increase in the compressibility coefficient of the domain state: coefficient oscillations were more than 100 times larger than the value predicted by the standard theory. The observed relation between magnetization current and deformation led us to conclude that the compressibility of the metal was fully determined by conduction electrons. Magnetostriction then exactly compensated Fermi level oscillations. The position of the Fermi level therefore remained constant under magnetic field variations. In addition, the domain wall thickness had to increase as the plate grew thicker.     

Ideal and resistive magnetohydrodynamic modes

This paper gives a further discussion of the analytical properties of both discrete and continuous Alfven wave spectra in an incompressible as well as compressible plasma. Although the continuous MHD modes produced by a well-behaved initial perturbation decay according to a power law, some singular solutions exist and are found to behave differently. In particular, it is possible to exhibit the existence of a new continuous mode which decays exponentially, and not as an inverse power of time, and this exponential damping is not the consequence of a continuous variation of the magnetic field. Even the set of discrete magnetohydrodynamic modes is shown to be empty unless certain conditions are satisfied. Next, we consider resistive modes and give explicit solutions for them which are valid in the neighborhood of the Alfven resonance layer and discuss their implications for plasma heating schemes. Finally, we study discrete and continuous Alfven wave spectra in a compressible plasma and discuss how they behave differently from those in an incompressible plasma. In particular, we show that though compressibility of the plasma is responsible for the slow mode continuum, strong compressibility will eliminate it. The discrete modes in a compressible plasma undergo an exponential damping even in an ideal plasma if the compressibility is strong.     

On the hydrodynamic sound in polarized Fermi liquids

The velocity of sound for polarized Fermi liquids at frequencies intermediate between the inverse spin relaxation time and the inverse typical relaxation time is found via the kinetic equation. This velocity is not expressed by the static compressibility at a fixed magnetic field but at fixed spin polarization. The measurement of static quantities and this velocity allows one to determine the Landau parameters with l = 0 and the effective masses for the polarized liquid.     

磁性液体中非磁性小球与磁性纳米颗粒的相互作用及磁组装

利用磁性液体与聚苯乙烯小球溶液混合得到的复合磁性液体, 研究了聚苯乙烯小球和磁性纳米颗粒在外加磁场作用下的动力学过程. 实验结果表明, 当外加磁场的方向平行于样品平面时, 聚苯乙烯小球在沿着磁场的方向上表现出相互吸引而形成链状结构, 其动力学过程可分为聚苯乙烯小球被反磁化产生相互吸引而形成短链的快过程以及短链间相互吸引形成长链的慢过程; 当外加磁场的方向垂直于样品平面时, 相邻聚苯乙烯小球表现出排斥的相互作用而形成短程有序的二维结构, 当磁场强度增加到一定的阈值时, 聚苯乙烯小球和磁性纳米颗粒形成的团簇会产生相互吸引而组装成复合式的花瓣结构. 关键词： 磁性液体 磁组装 非磁性颗粒