Charge inversion,condensation and decondensation of DNA and polystyrene sulfonate by polyethylenimine

We study the formation and structure of stable electrostatic complexes between polyanions (DNA and poly(styrene-sulfonate)) and linear polyethylenimine. The charge ratio x of the mixture is tuned by varying the concentration of the polycation at constant concentration of polyanion. In agreement with recent theories, dynamic light scattering and electrophoretic mobility measurements show two distinct regimes of weak and strong complexation. At low polycation concentration, negatively charged small complexes involving a few polyanion chains are observed first. By further increasing x , these small complexes condense at a precise charge ratio x _c < 1 to form large anionic aggregates. The inversion of the charge of the condensed complexes coincides with the maximum of complexation and precedes the dissolution of the aggregates which occurs at a well-defined decondensation threshold x _d > 1. Above x _d , positively charged complexes containing again a few overcharged polyanion chains are observed. The macroscopic phase diagram is qualitatively well corroborated by AFM observation of the complexes. The influence of entropic effects is probed by varying parameters like concentration, polycation molecular weight and ionic strength. Structure of stable negatively charged complexes is investigated at higher concentration using Small Angle Neutron Scattering. In the condensed regime, we observe large soluble bundles with sharp interfaces where the local structure of the polyanions is preserved.     

On the spin of Solitons in 2+1 dimensional models

It is believed that the charged vortex in the Chern-Simons-Higgs model can have fractional spin, since the extra angular momentum of the static vortex calculated from the classical energy-momentum tensor is nonzero. We re-examine the spin of the charged vortex by use of quantum mechanical method, by which the baby skyrmion in theO(3) nonlinear -model with the Hopf term is pointed out to have fractional spin. It is shown that the spin of the charged vortex obtained from the quantum mechanical argument does not necessarily coincide with the value of classical extra angular momentum. Moreover, it is found that its value is not unique, since it is one of quantities which depend on the gauge condition of the Chern-Simons gauge field.     

Electric Charges in Superconducting Mesoscopic Samples

The distribution of the electric charge density in mesoscopic superconducting disks and cylinders is studied within the phenomenological Ginzburg-Landau approach. We found that even in the Meissner state the mesoscopic sample exhibits a non-uniform charge distribution such that a region near the sample edge becomes negatively charged. When vortices are inside the sample there is a superposition of the negative charge located at the vortex core and this Meissner charge, and, as a result, the charge at the sample edge changes sign as a function of the applied magnetic field.     

La0.3Ca0.7Mn1－xVxO3体系的有序相和再入型自旋玻璃行为研究

通过对La_0.3Ca_0.7Mn_1－xV_xO₃(x=0.05,0.10,0.134,0.20)体系的M-T曲线、ρ-T曲线、ESR谱的测量,研究了Mn位掺V对La_0.3Ca_0.7MnO₃体系电荷序和自旋序的影响.结果表明,当0.05≤x≤0.134时, 体系存在电荷有序(CO)相,其自旋序随温度降低发生顺磁(PM)-电荷有序(CO)-反铁磁(AFM)变化.当x＝0.20时,CO相逐步融化,在40 K发生自旋玻璃转变,表现出再入型的自旋玻璃行为,低温下的基态存在着多种复杂的磁相互作用之间的竞争机理. 关键词： 电荷有序 自旋序 相分离 再入型自旋玻璃行为     

Electron Spin Resonance Study on the Photoinduced Electron Transfer in Chlorophyll a in Reconstituted Lipid Bilayer Vesicles

Abstract  

The photoinduced electron transfer from chlorophyll a through the interface of positively charged dioctadecyltrimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC) and negatively charged dihexadecylphosphate (DHP) headgroup of the lipid bilayers was studied. The photoinduced radicals were identified by electron spin resonance (ESR) and radical yields of chlorophyll a were determined by double integration of the ESR spectra. The formation of vesicles was identified indirectly by measuring change of the λ _max value of optical absorption spectrophotometer from diethyl ether solution to vesicle solutions, and observed directly with scanning and transmission electron microscopic images. The interaction distance between chlorophyll a and interface water (D₂O) determined by deuterium modulation depth with electron spin echo modulation (ESEM) showed a decreasing order DODAC > DPPC > DHP. The interface charge of each vesicle was determined with zeta potential measurement. The interface charge of the lipid bilayers affected the radical yields of chlorophyll a more critically than the interaction distance between chlorophyll a and interface water.     

Generation and gyroscopic quasi-relativistic dynamics of antiferromagnetic vortices in domain walls of yttrium orthoferrite

An unusual nonlinear relation between the velocity of an antiferromagnetic (AFM) vortex along a domain wall (DW) on the DW velocity is detected. This relation has a maximum whose position depends on the topological charge of the vortex. As the DW velocity increases from the value corresponding to the maximum to its limiting value, the AFM-vortex velocity decreases and tends to zero. The total AFM-vortex velocity increases nonlinearly with the DW velocity and levels off at 20 km/s, which is equal to the velocity of spin waves in the linear section of their dispersion law. The experimental data are approximated satisfactorily. The dynamics of AFM vortices in DWs of yttrium orthoferrite, just as the dynamics of the DWs, is quasi-relativistic and gyroscopic.     

Quasiparticle states at a d-wave vortex core in high- T(c) superconductors: induction of local spin density wave order

The local density of states (LDOS) at the vortex lattice cores in a high- T(c) superconductor is studied by using a self-consistent mean-field theory including interactions for both antiferromagnetism (AF) and d-wave superconductivity (DSC). In a zero-field optimally doped sample the AF order is completely suppressed while DSC prevails. In the mixed state, we show that the local AF-like spin density wave order appears near the vortex core and acts as an effective local magnetic field on electrons via Zeeman coupling. As a result, the LDOS at the core exhibits a double-peak structure near the Fermi level that is in good agreement with recent scanning tunneling microscopy observations.     

Explanation of atomic displacement around lattice vacancies in diamond based on electron delocalization

The relationship between unpaired electron delocalization and nearest-neighbor atomic relaxations in the vacancies of diamond has been determined in order to understand the microscopic reason behind the neighboring atomic relaxation. The Density Functional Theory (DFT) cluster method is applied to calculate the single-electron wavefunction of the vacancy in different charge states. Depending on the charge and spin state of the vacancies, at outward relaxations, 84-90% of the unpaired electron densities are localized on the first neighboring atoms. The calculated spin localizations on the first neighboring atoms in the ground state of the negatively charged vacancy and in the spin quintet excited state of the neutral vacancy are in good agreement with Electron Paramagnetic Resonance (EPR) measurements. The calculated spin localization of the positively charged vacancy contrasts with the tentative assignment of the NIRIM-3 EPR signal to this center in (p-type) semiconductor diamond. The sign of the lattice relaxation in the diamond vacancy is explained based on the effect of electron delocalization on nearest-neighbor ion-ion screening, and also its effect on the bond length of neighboring atoms.     

Experimental evidence of coupling interaction between charge ordering and spin ordering

In order to experimentally probe into the complicated interaction between charge ordering and spin ordering in manganites,two sets of samples Nd0.5Sr0.5Mn1-xGaxO3(NSMGO) and Nd 0.5Sr0.5Mn1-y CryO3(NSMCO)(0.0 x,y 0.075),have been studied by means of electrical transport,magnetization,electron spin resonance and transmission electron microscopy analysis.By comparing the influence of Cr-doping and Ga-doping in the Nd0.5Sr0.5MnO3(NSMO) system,large difference between the evolution of charge ordering temperature T co in the Cr-doping and the Ga-doping cases is found.In the NSMCO system,the CE-type antiferromagnetic(AFM)/charge ordering(CO) phase disappears with only 2.5 percent Cr doping;but in the NSMGO system,the CE-type AFM/CO phase always exists.This phenomenon indicates that the charge ordering formation is dominated by the spin ordering.As a result,it is experimentally proved that there is strong coupling interaction between charge ordering and spin ordering in NSMO system.     

Ferromagnetism and colossal magnetoresistance from phase competition

We report a multicomponent theory for the coexistence of charge ordering (CO), and antiferromagnetic (AFM) and ferromagnetic (FM) spin ordering. This kind of state is invoked for manganites by Moreo et al., Science 283, 2034 (1999) and observed in recent experiments. We show that doping an AFM or CO state always generates a FM component. FM, AFM, and CO necessarily coexist in a particle-hole asymmetric system. Melting of large AFM-CO orders by small magnetic fields and colossal magnetoresistance (CMR) arise whenever the CO and AFM order parameters have similar magnitude and momentum structure. Hole doping favors FM metallic states while electron doping favors AFM-CO states, as in CMR manganites.     

Superconducting strings

It is known that certain spontaneously broken gauge theories give rise to stable strings or vortex lines. In this paper it is shown that under certain conditions such strings behave like superconducting wires whose passage through astrophysical magnetic fields would generate a variety of striking and perhaps observable effects. The superconducting charge carriers may be either bosons (if a charged Higgs field has an expectation value in the core of the string) or fermions (if charged fermions are trapped in zero modes along the string, as is known to occur in certain circumstances). They might be observable as synchrotron sources or as sources of high-energy cosmic rays. If the charge carriers are ordinary quarks and leptons, the strings have important baryon number violating interactions with magnetic fields; such a string, traversing a galactic magnetic field of 10^?6 G, creates baryons (or antibaryons) at a rate of order 10¹² particles/cm of string per second.     

Magnetization dynamics: ultra-fast and ultra-small

Ultrafast magnetic processes are of great scientific interest but also form the basis of high density magnetic recording applications. We demonstrate the uniqueness of time resolved, high resolution magnetic X-ray microscopy, and show that the motion of a magnetic vortex core can be imaged. The vortex core direction is hidden to most experimental techniques, but has a decisive influence on the dynamics of the magnetic structure.We imaged the switching of a ferromagnetic nanostructure by a spin polarized current pulse using time resolved X-ray microscopy. As opposed to the common uniform switching process due to Néel and Stoner–Wohlfarth, the magnetization in spin injection devices does not switch uniformly, but involves the motion of a magnetic vortex. To cite this article: Y. Acremann, C. R. Physique 9 (2008).     

Magnetic phase diagram of an extended Hubbard model at half filling: Possible application for strongly correlated iron pnictides

We study the magnetic phase diagram within an extended half-filled Hubbard model, focusing on the roles of the next-nearest-neighbor (NNN) and the next-next-nearest-neighbor (3rd NN) hoppings in the magnetic configurations. We find that due to the spin frustration from the long range hopping and the competition between long-range hopping and Coulomb correlation, the striped antiferromagnetic (AFM) phase is stable when the NNN hopping is dominant, while the bicollinear AFM phase is robust when the 3rd NN hopping is considerably large. The triple points are found in various magnetic phase diagrams. Possible applications of the present theory on intermediately correlated LaFeAsO and strongly correlated FeTe are discussed.     

Ferrimagnetic ground state of a phenylene polymer with organic radicals

A ferrimagnetic polymer with m-phenylene skeleton as coupling unit is studied with the Hubbard model in the self-consistent mean-field theory. The ferrimagnetic ground state with a total spin S = 1 per unit cell is obtained and originates from the antiferromagnetic correlations between the nearest neighbors. If the on-site electron-electron repulsions at the radical sites and at the phenylene ring sites are different, the gap in energy band structure may disappear and the ferrimagnetic ground state becomes unstable. The charge density and spin density can transfer between the radical sites and the phenylene ring sites due to the competition between the hopping integral and the on-site repulsion at different sites. Received 15 July 2002 Published online 31 December 2002     

基于AFM的固液界面表面电荷密度测量方法

固液界面的表面电荷会影响微纳流体系统的流体阻力,因此如何测量固液界面的表面电荷密度以及分析表面电荷的产生机理对于研究表面电荷对流体阻力的影响具有较大的意义。提出了一种基于接触式AFM的固液界面表面电荷密度测量方法。基于该方法测量了浸在去离子水和0.01 mol/L的NaCl溶液中的高硼硅玻璃和二氧化硅样本的表面电荷密度,并研究了溶液pH值对表面电荷的影响。研究结果表明高硼硅玻璃和二氧化硅由于表面硅烷基的电离带负电。溶液pH值和离子浓度的增加都会增加浸在去离子水和0.01 mol/L的NaCl溶液中高硼硅玻璃和二氧化硅的表面电荷密度的绝对值。     

Stripes and superconductivity in a one-dimensional self-consistent model

We show that many observable properties of high-temperature superconductors can be obtained in the framework of a one-dimensional self-consistent model with included superconducting correlations. Analytical solutions for spin, charge, and superconductivity order parameters are found. The ground state of the model at low hole doping is a spin-charge solitonic superstructure. Increased doping leads to a transition to the superconducting phase. There is a region of doping where superconductivity, spin density wave, and charged stripe structure coexist. The charge density modulation appears in the vicinity of vortices (kinks in the 1D model) in the superconducting state.     

Charge and spin order on the triangular lattice: NaxCoO2 at x=0.5

The nature of electronic states due to strong correlation and geometric frustration on the triangular lattice is investigated in connection to the unconventional insulating state of NaxCoO2 at x=0.5. We study an extended Hubbard model using a spatially unrestricted Gutzwiller approximation. We find a new class of charge and spin ordered states at x=1/3 and x=0.5 where antiferromagnetic (AFM) frustration is alleviated via weak charge inhomogeneity. At x=0.5, we show that the square root of 3a x 2a off-plane Na dopant order induces weak square root of 3a x 1a charge order in the Co layer. The symmetry breaking enables successive square root of 3a x 1a AFM and 2a x 2a charge- or spin-ordering transitions at low temperatures. The Fermi surface is truncated by the 2a x 2a hexagonal zone boundary into small electron and hole pockets. We study the phase structure and compare to recent experiments.     

Low temperature limit of the vortex core radius and the kramer-pesch effect in NbSe2

Muon spin rotation ( &mgr;SR) has been used to measure the magnetic field distribution in the vortex state of the type-II superconductor NbSe2 ( T(c) = 7.0 K) below T = 2 K. The distribution is consistent with a highly ordered hexagonal vortex lattice with a well resolved high-field cutoff associated with the finite size of the vortex cores. The temperature dependence of the core radius is much weaker than the temperature dependence predicted from the Bogoliubov-de Gennes theory. Furthermore, the vortex radius measured by &mgr;SR near the low temperature quantum limit is about an order of magnitude larger than predicted.     

Vortex dynamics and correlated disorder in high-Tc superconductors

We develop a theory for the vortex motion in the presence of correlated disorder in the form of twin boundaries and columnar defects. Mapping vortex trajectories onto boson world lines enables us to establish the duality of the vortex transport in systems with correlated disorder and the hopping conductivity of charged particles in 2D systems. A glassy-like dynamics of the vortex lines with zero linear resistivity and strongly nonlinear current-voltage behavior as V ∝ exp(-const/J^μ) in a Bose glass state is predicted.     

Vortex charges in high-temperature superconductors

Based on a model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconductivity interactions, the vortex charge is investigated by solving the Bogoliubov-de Gennes equations. We found that the vortex charge is negative when a sufficient strength of AF order is induced inside the vortex core; otherwise, it is positive. By tuning the on-site Coulomb repulsion U or the doping parameter delta, a transition between the positive and negative vortex charges may occur. The vortex charge at optimal doping has also been studied as a function of magnetic field. Recent NMR and Hall effect experiments may be understood in terms of the present results.