Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors

We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation in the vortex state of type-II superconductors, with a special focus on the connection between the gap anisotropy and the oscillation damping. Numerical calculations for three different gap structures clearly indicate that the average gap along extremal orbits is relevant for the magnitude of the extra damping, thereby providing a support for experimental efforts to probe gap anisotropy through the dHvA signal. We also derive an analytic formula for the extra damping which gives a good fit to the numerical results.Comment: 5 pages, 1 figure, changes in Introductio

Theory of Flux-Flow Resistivity near Hc2H_{c2} for s-wave Type-II Superconductors

This paper presents a microscopic calculation of the flux-flow resistivity $\rho_{f}$ for s-wave type-II superconductors with arbitrary impurity concentrations near the upper critical field $H_{c2}$. It is found that, as the mean free path $l$ becomes longer, $\rho_{f}$ increases gradually from the dirty-limit result of Thompson [Phys. Rev. B{\bf 1}, 327 (1970)] and Takayama and Ebisawa [Prog. Theor. Phys. {\bf 44}, 1450 (1970)]. The limiting behaviors suggest that $\rho_{f}(H)$ at low temperatures may change from convex downward to upward as $l$ increases, thus deviating substantially from the linear dependence $\rho_{f}\propto H/H_{c2}$ predicted by the Bardeen-Stephen theory [Phys. Rev. {\bf 140}, A1197 (1965)]

Properties of Nambu-Goldstone Bosons in a Single-Component Bose-Einstein Condensate

We theoretically study the properties of Nambu-Goldstone bosons in an interacting single-component Bose-Einstein condensate (BEC). We first point out that the proofs of Goldstone's theorem by Goldstone, et al. [Phys. Rev. {\bf 127} (1962) 965] may be relevant to distinct massless modes of the BEC: whereas the first proof deals with the poles of the single-particle Green's function $\hat{G}$, the second one concerns those of the two-particle Green's function. Thus, there may be multiple Nambu-Goldstone bosons even in the single-component BEC with broken U(1) symmetry. The second mode turns out to have an infinite lifetime in the long-wavelength limit in agreement with the conventional viewpoint. In contrast, the first mode from $\hat{G}$, i.e., the Bogoliubov mode in the weak-coupling regime, is shown to be a "bubbling" mode fluctuating temporally out of and back into the condensate. The substantial lifetime originates from an "improper" structure of the self-energy inherent in the BEC, which has been overlooked so far and will be elucidated here, and removes various infrared divergences pointed out previously.Comment: 9 pages, 6 gigure

Does event structure influence children's motion event expressions

This study focuses on understanding of event structure, in particular therelationship between Manner and Path. Narratives were elicited from twenty 3-year-olds and twenty adults using 6 animated motion events that were divided into two groups based on Goldberg's (1997) distinction between causal (Manner-inherent; e.g. roll down) and non-causal (Manner-incidental; e.g. spin while going up) relationships between Manner and Path. The data revealed that adults and children are sensitive to differences between inherent and incidental Manner. Adults significantly reduced use of canonical syntactic constructions for Manner-incidental events, employing other constructions. Children, however, while significantly reducing use of canonical syntactic constructionsfor Manner-incidental events, did not exploit alternative constructions. Instead, they omitted Manner from their speech altogether. A follow-up lexical task showed that children had knowledge of all omitted Manners. Given that this strategic omission of Manner is not lexically motivated, the results are discussed in relation to implications for pragmatics and memory load

Self-Consistent Approximations for Superconductivity beyond the Bardeen-Cooper-Schrieffer Theory

We develop a concise self-consistent perturbation expansion for superconductivity where all the pair processes are naturally incorporated without drawing "anomalous" Feynman diagrams. This simplification results from introducing an interaction vertex that is symmetric in the particle-hole indices besides the ordinary space-spin coordinates. The formalism automatically satisfies conservation laws, includes the Luttinger-Ward theory as the normal-state limit, and reproduces the Bardeen-Cooper-Schrieffer theory as the lowest-order approximation. It enables us to study the thermodynamic, single-particle, two-particle, and dynamical properties of superconductors with competing fluctuations based on a single functional $\Phi[\hat{G}]$ of Green's function $\hat{G}$ in the Nambu space. Specifically, we derive closed equations in the FLEX-S approximation, i.e., the fluctuation exchange approximation for superconductivity with all the pair processes, which contains extra terms besides those in the standard FLEX approximation.Comment: 14 pages, 6 figure

TeV Gamma Ray Emission from Southern Sky Objects and CANGAROO Project

We report recent results of the CANGAROO Collaboration on very high energy gamma ray emission from pulsars, their nebulae, SNR and AGN in the southern sky. Observations are made in South Australia using the imaging technique of detecting atmospheric Cerenkov light from gamma rays higher than about 1 TeV. The detected gamma rays are most likely produced by the inverse Compton process by electrons which also radiate synchrotron X-rays. Together with information from longer wavelengths, our results can be used to infer the strength of magnetic field in the emission region of gamma rays as well as the energy of the progenitor electrons. A description of the CANGAROO project is also given, as well as details of the new telescope of 7 m diameter which is scheduled to be in operation within two years.Comment: 5 pages, 1 figure, LaTeX 2.09 with aipproc.sty & epsfig.sty, to appear in proceedings of the 4th Compton Symposium, Williamsburg, 199