Motion of Vacancies in a Pinned Vortex Lattice: Origin of the Hall Anomaly

Physical arguments are presented to show that the Hall anomaly is an effect of the vortex many-body correlation rather than that of an individual vortex. Quantitatively, the characteristic energy scale in the problem, the vortex vacancy formation energy, is obtained for thin films. At low temperatures a scaling relation between the Hall and longitudinal resistivities is found, with the power depending on sample details. Near the superconducting transition temperature and for small magnetic fields the Hall conductivity is found to be proportional to the inverse of the magnetic field and to the quadratic of the difference between the measured and the transition temperatures.Comment: minor change

A Scenario to the Anomalous Hall Effect in the Mixed State of Superconductors

We argue that the motion of vacancies in a pinned vortex lattice may dominate the contribution to the Hall effect in an appropriate parameter regime for a superconductor. Based on this consideration a model is constructed to explain the anomalous Hall effect without any modification of the basic vortex dynamic equation. Quantitative predictions are obtained. Present model can be directly tested by an observation of the vacancy motion.Comment: latex, 6 pages (Presented at the Miami High Tc Conf., Jan 5-11, 1995. To appear at J. Supercond.

On the action potential as a propagating density pulse and the role of anesthetics

The Hodgkin-Huxley model of nerve pulse propagation relies on ion currents through specific resistors called ion channels. We discuss a number of classical thermodynamic findings on nerves that are not contained in this classical theory. Particularly striking is the finding of reversible heat changes, thickness and phase changes of the membrane during the action potential. Data on various nerves rather suggest that a reversible density pulse accompanies the action potential of nerves. Here, we attempted to explain these phenomena by propagating solitons that depend on the presence of cooperative phase transitions in the nerve membrane. These transitions are, however, strongly influenced by the presence of anesthetics. Therefore, the thermodynamic theory of nerve pulses suggests a explanation for the famous Meyer-Overton rule that states that the critical anesthetic dose is linearly related to the solubility of the drug in the membranes.Comment: 13 pages, 8 figure

Electrostatics of Vortices in Type II Superconductors

In a type II superconductor the gap variation in the core of a vortex line induces a local charge modulation. Accounting for metallic screening, we determine the line charge of individual vortices and calculate the electric field distribution in the half space above a field penetrated superconductor. The resulting field is that of an atomic size dipole ${\bf d} \sim e a_{{\rm B}} {\bf {\hat z}}$, $a_{{\rm B}} = \hbar^2/m e^2$ is the Bohr radius, acting on a force microscope in the pico to femto Newton range.Comment: 9 pages, late

Exchange Effects in the Invar Hardening: Fe0.65Ni0.35Fe_{0.65}Ni_{0.35} as a test case

An increase of the critical resolved shear stress of Invar alloys (Invar hardening) with a lowering temperature is explained. The effect is caused by a growth of the exchange interaction between dangling $d$-electron states of dislocation cores and paramagnetic obstacles (e.g., Ni atoms in FeNi alloys) which occurs below the Curie temperature. The spins of the two electrons align along the magnetization due to the exchange interaction with the surrounding atoms of the ferromagnetic. The exchange interaction between the dislocations and obstacles is enhanced in Invars due to a strong growth of the magnetic moments of atoms under the action of elastic strains near the dislocation cores. Parameters characterizing the exchange interaction are determined for the case of the Fe$_{0.65}$Ni$_{0.35}$ Invar. The influence of the internal magnetic field on the dislocation detachment from the obstacles is taken into account. The obtained temperature dependence of the critical resolved shear stress in the Fe$_{0.65}$Ni$_{0.35}$ Invar agrees well with the available experimental data. Experiments facilitating a further check of the theoretical model are suggested.Comment: 8 pages, 2 figure

Soft Stylus Probes for Scanning Electrochemical Microscopy

A soft stylus microelectrode probe has been developed to carry out scanning electrochemical microscopy (SECM) of rough, tilted, and large substrates in contact mode. It is fabricated by first ablating a microchannel in a polyethylene terephthalate thin film and filling it with a conductive carbon ink. After curing the carbon track and lamination with a polymer film, the V- shaped stylus was cut thereby forming a probe, with the cross section of the carbon track at the tip being exposed either by UVphotoablation machining or by blade cutting followed by polishing to produce a crescent moon- shaped carbon microelectrode. The probe properties have been assessed by cyclic voltammetry, approach curves, and line scans over electrochemically active and inactive substrates of different roughness. The influence of probe bending on contact mode imaging was then characterized using simple patterns. Boundary element method simulations were employed to rationalize the distance-dependent electrochemical response of the soft stylus probes

Flux-Induced Vortex in Mesoscopic Superconducting Loops

We predict the existence of a quantum vortex for an unusual situation. We study the order parameter in doubly connected superconducting samples embedded in a uniform magnetic field. For samples with perfect cylindrical symmetry, the order parameter has been known for long and no vortices are present in the linear regime. However, if the sample is not symmetric, there exist ranges of the field for which the order parameter vanishes along a line, parallel to the field. In many respects, the behavior of this line is qualitatively different from that of the vortices encountered in type II superconductivity. For samples with mirror symmetry, this flux-induced vortex appears at the thin side for small fluxes and at the opposite side for large fluxes. We propose direct and indirect experimental methods which could test our predictions.Comment: 6 pages, Latex, 4 figs., uses RevTex, extended to situations far from cylindrical symmetr

The influence of anesthetics, neurotransmitters and antibiotics on the relaxation processes in lipid membranes

In the proximity of melting transitions of artificial and biological membranes fluctuations in enthalpy, area, volume and concentration are enhanced. This results in domain formation, changes of the elastic constants, changes in permeability and slowing down of relaxation processes. In this study we used pressure perturbation calorimetry to investigate the relaxation time scale after a jump into the melting transition regime of artificial lipid membranes. This time corresponds to the characteristic rate of domain growth. The studies were performed on single-component large unilamellar and multilamellar vesicle systems with and without the addition of small molecules such as general anesthetics, neurotransmitters and antibiotics. These drugs interact with membranes and affect melting points and profiles. In all systems we found that heat capacity and relaxation times are related to each other in a simple manner. The maximum relaxation time depends on the cooperativity of the heat capacity profile and decreases with a broadening of the transition. For this reason the influence of a drug on the time scale of domain formation processes can be understood on the basis of their influence on the heat capacity profile. This allows estimations of the time scale of domain formation processes in biological membranes.Comment: 12 pages, 6 figure

Phase transitions in biological membranes

Native membranes of biological cells display melting transitions of their lipids at a temperature of 10-20 degrees below body temperature. Such transitions can be observed in various bacterial cells, in nerves, in cancer cells, but also in lung surfactant. It seems as if the presence of transitions slightly below physiological temperature is a generic property of most cells. They are important because they influence many physical properties of the membranes. At the transition temperature, membranes display a larger permeability that is accompanied by ion-channel-like phenomena even in the complete absence of proteins. Membranes are softer, which implies that phenomena such as endocytosis and exocytosis are facilitated. Mechanical signal propagation phenomena related to nerve pulses are strongly enhanced. The position of transitions can be affected by changes in temperature, pressure, pH and salt concentration or by the presence of anesthetics. Thus, even at physiological temperature, these transitions are of relevance. There position and thereby the physical properties of the membrane can be controlled by changes in the intensive thermodynamic variables. Here, we review some of the experimental findings and the thermodynamics that describes the control of the membrane function.Comment: 23 pages, 15 figure

Theory of superconductor with kappa close to 1/sqrt{2}

As was firstly shown by E. Bogomolny, the critical Ginzburg-Landay (GL) parameter kappa =1/sqrt{2} at which a superconductor changes its behavior from type-I to type-II, is the special highly degenerate point where Abrikosov vortices do not interact and therefore all vortex states have the same energy. Developing a secular perturbation theory we studied how this degeneracy is lifted when kappa is slightly different from 1\sqrt{2} or when the GL theory is extended to the higher in T-Tc terms. We constructed a simple secular functional, that depends only on few experimentally measurable phenomenological parameters and therefore is quite efficient to study the vortex state of superconductor in this transitional region of kappa. Basing on this, we calculated such vortex state properties as: critical fields, energy of the normal-superconductor interface, energy of the vortex lattice, vortex interaction energy etc. and compared them with previous results that were based on bulky solutions of GL equations.Comment: Revtex, 14 pages, 4 postscript pictures embedded in the tex