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.

Redox properties and electron paramagnetic resonance spectroscopy of the transition state complex of Azotobacter vinelandii nitrogenase

AbstractNitrogenase is a two-component metalloenzyme that catalyzes a MgATP hydrolysis driven reduction of substrates. Aluminum fluoride plus MgADP inhibits nitrogenase by stabilizing an intermediate of the on-enzyme MgATP hydrolysis reaction. We report here the redox properties and electron paramagnetic resonance (EPR) signals of the aluminum fluoride-MgADP stabilized nitrogenase complex of Azotobacter vinelandii. Complex formation lowers the midpoint potential of the [4Fe-4S] cluster in the Fe protein. Also, the two-electron reaction of the unique [8Fe-7S] cluster in the MoFe protein is split in two one-electron reactions both with lower midpoint potentials. Furthermore, a change in spin-state of the two-electron oxidized [8Fe-7S] cluster is observed. The implications of these findings for the mechanism of MgATP hydrolysis driven electron transport within the nitrogenase protein complex are discussed

Superfield Formulation for Non-Relativistic Chern-Simons-Matter Theory

We construct a superfield formulation for non-relativistic Chern-Simons-Matter theories with manifest dynamical supersymmetry. By eliminating all the auxiliary fields, we show that the simple action reduces to the one obtained by taking non-relativistic limit from the relativistic Chern-Simons-Matter theory proposed in the literature. As a further application, we give a manifestly supersymmetric derivation of the non-relativistic ABJM theory.Comment: 18 page

Transformation of in-plane ρ(T)\rho (T) in YBa2Cu3O7−δYBa_{2}Cu_{3}O_{7-\delta} at fixed oxygen content

This paper reveals the origin of variation in the magnitude and temperature dependence of the normal state resistivity frequently observed in different YBCO single crystal or thin film samples with the same $T_{c}$. We investigated temperature dependence of resistivity in $YBa_{2}Cu_{3}O_{7-\delta}$ thin films with 7- $\delta = 6.95$ and 6.90, which were subjected to annealing in argon at 400-420 K ($120-140^{o}C$). Before annealing these films exhibited a non-linear $\rho_{ab}(T)$, with a flattening below 230 K, similar to $\rho_{b}(T)$ and $\rho_{ab}(T)$ observed in untwinned and twinned YBCO crystals, respectively. For all films the annealing causes an increase of resistivity and a transformation of $\rho_{ab}(T)$ from a non-linear dependence towards a more linear one (less flattening). In films with 7- $\delta = 6.90$ the increase of resistivity is also associated with an increase in $T_{c}$. We proposed the model that provides an explanation of these phenomena in terms of thermally activated redistribution of residual O(5) oxygens in the chain-layer of YBCO. Good agreement between the experimental data for $\rho_{ab}(t,T)$, where t is the annealing time, and numerical calculations was obtained.Comment: 8 pages, 9 figures, submitted to PR

Temperature-scaling behavior of the Hall conductivity for Hg-based superconducting thin films

The Hall conductivities of HgBa_{2}CaCu_{2}O_{6+\delta}and HgBa_{2}Ca_{2}Cu_{3}O_{8+\delta} thin films are investigated for a magnetic field parallel to the c axis. The mixed-state Hall conductivity for these compounds is well described by \sigma_{xy}=C_{1}/H+C_{2}+C_{3}H. The prefactor C_1 shows a temperature dependence of the form C_1 = A(1-t)^n near T_c, where t=T/T_c is the reduced temperature. Contrary to the previous results, C_2 also follows a temperature-scaling behavior similar to that of the coefficient C_1. The observed value of n = 1.8 - 2.3 is comparable to the previously observed values for YBa_{2}Cu_{3}O_{7-\delta} and La_{2-x}Sr_{x}CuO_{4}.Comment: 5 pages, 4 eps figure

Chemical Potential Shift in Nd2−x_{2-x}Cex_{x}CuO4_{4}: Contrasting Behaviors of the Electron- and Hole-Doped Cuprates

We have studied the chemical potential shift in the electron-doped superconductor Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ by precise measurements of core-level photoemission spectra. The result shows that the chemical potential monotonously increases with electron doping, quite differently from La$_{2-x}$Sr$_{x}$CuO$_{4}$, where the shift is suppressed in the underdoped region. If the suppression of the shift in La$_{2-x}$Sr$_{x}$CuO$_{4}$ is attributed to strong stripe fluctuations, the monotonous increase of the chemical potential is consistent with the absence of stripe fluctuations in Nd$_{2-x}$Ce$_{x}$CuO$_{4}$. The chemical potential jump between Nd$_{2}$CuO$_{4}$ and La$_{2}$CuO$_{4}$ is found to be much smaller than the optical band gaps.Comment: 4 pages, 5 figure

Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors

Based on existing theoretical model and by considering our longitudinal nonlinear response function, we derive a nonliear equation in which the mixed state Hall resistivity can be expressed as an analytical function of magnetic field, temperature and applied current. This equation enables one to compare quantitatively the experimental data with theoretical model. We also find some new scaling relations of the temperature and field dependency of Hall resistivity. The comparison between our theoretical curves and experimental data shows a fair agreement.Comment: 4 pages, 3 figure

Density-matrix formalism with three-body ground-state correlations

A density-matrix formalism which includes the effects of three-body ground- state correlations is applied to the standard Lipkin model. The reason to consider the complicated three-body correlations is that the truncation scheme of reduced density matrices up to the two-body level does not give satisfactory results to the standard Lipkin model. It is shown that inclusion of the three-body correlations drastically improves the properties of the ground states and excited states. It is pointed out that lack of mean-field effects in the standard Lipkin model enhances the relative importance of the three-body ground-state correlations. Formal aspects of the density-matrix formalism such as a relation to the variational principle and the stability condition of the ground state are also discussed. It is pointed out that the three-body ground-state correlations are necessary to satisfy the stability condition

Confinement of Spin and Charge in High-Temperature Superconductors

By exploiting the internal gauge-invariance intrinsic to a spin-charge separated electron, we show that such degrees of freedom must be confined in two-dimensional superconductors experiencing strong inter-electron repulsion. We also demonstrate that incipient confinement in the normal state can prevent chiral spin-fluctuations from destroying the cross-over between strange and psuedo-gap regimes in under-doped high-temperature superconductors. Last, we suggest that the negative Hall anomaly observed in these materials is connected with this confinement effect.Comment: 12 pages, 1 postscript figure, to appear in PRB (RC), May 199

Nernst Effect in Electron-Doped Pr2−x_{2-x}Cex_{x}CuO4_4

The Nernst effect of Pr$_{2-x}$Ce$_{x}$CuO$_4$ (x=0.13, 0.15, and 0.17) has been measured on thin film samples between 5-120 K and 0-14 T. In comparison to recent measurements on hole-doped cuprates that showed an anomalously large Nernst effect above the resistive T$_c$ and H$_{c2}$ \cite{xu,wang1,wang2,capan}, we find a normal Nernst effect above T$_c$ and H$_{c2}$ for all dopings. The lack of an anomalous Nernst effect in the electron-doped compounds supports the models that explain this effect in terms of amplitude and phase fluctuations in the hole-doped cuprates. In addition, the H$_{c2}$(T) determined from the Nernst effect shows a conventional behavior for all dopings. The energy gap determined from H$_{c2}$(0) decreases as the system goes from under-doping to over-dopingin agreement with the recent tunnelling experiments