Proximity Effect in Nb/Au/CoFe Trilayers

We have investigated the superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of Au and CoFe thicknesses. Without the CoFe layer the superconducting critical temperatures of Nb/Au bilayers as a function of Au thickness follow the well-known proximity effect between a superconductor and a normal metal. The superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of Au thickness exhibit a rapid initial increase in the small Au thickness region and increase slowly to a limiting value above this region, accompanied by a small oscillation of Tc. On the other hand, the superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of CoFe thickness show non-monotonic behavior with a shallow dip feature. We analyzed the Tc behavior in terms of Usadel formalism and found that most features are consistent with the theory, although the small oscillation of Tc as a function of the Au thickness cannot be accounted for. We have also found quantitative values for the two interfaces: Nb/Au and Au/CoFe.Comment: 25 pages, 6 figure

Spin-triplet pairing instability of the spinon Fermi surface in a U(1) spin liquid

Recent experiments on the organic compound \kappa-(ET)_2Cu_2(CN)_3 have provided a promising example of a two dimensional spin liquid state. This phase is described by a two-dimensional spinon Fermi sea coupled to a U(1) gauge field. We study Kohn-Luttinger-like pairing instabilities of the spinon Fermi surface due to singular interaction processes with twice-the-Fermi-momentum transfer. We find that under certain circumstances the pairing instability occurs in odd-orbital-angular-momentum/spin-triplet channels. Implications to experiments are discussed.Comment: 4 pages, 1 figur

Generalized BFT Formalism of Electroweak Theory in the Unitary Gauge

We systematically embed the SU(2)$\times$U(1) Higgs model in the unitary gauge into a fully gauge-invariant theory by following the generalized BFT formalism. We also suggest a novel path to get a first-class Lagrangian directly from the original second-class one using the BFT fields.Comment: 14 pages, Latex, no figure

P-wave Pairing and Colossal Magnetoresistance in Manganese Oxides

We point out that the existing experimental data of most manganese oxides show the {\sl frustrated} p-wave superconducting condensation in the ferromagnetic phase in the sense that the superconducting coherence is not long enough to cover the whole system. The superconducting state is similar to the $A_{1}$ state in superfluid He-3. The sharp drop of resistivity, the steep jump of specific heat, and the gap opening in tunneling are well understood in terms of the p-wave pairing. In addition, colossal magnetoresistance (CMR) is naturally explained by the superconducting fluctuations with increasing magnetic fields. The finite resistivity may be due to some magnetic inhomogeneities. This study leads to the possibility of room temperature superconductivity.Comment: LaTex, 14 pages, For more information, please send me an e-mail. e-mail adrress : [email protected]

Weak Localization Effect in Superconductors

We study the effect of weak localization on the transition temperatures of superconductors using time-reversed scattered state pairs, and find that the weak localization effect weakens electron-phonon interactions. With solving the BCS $T_{c}$ equation, the calculated values for $T_c$ are in good agreement with experimental data for various two- and three-dimensional disordered superconductors. We also find that the critical sheet resistance for the suppression of superconductivity in thin films does not satisfy the universal behavior but depends on sample, in good agreement with experiments. but depends on sample, in good agreement with experiments.Comment: 14 pages, Revtex, 5 ps figure

Hamiltonian Embedding of SU(2) Higgs Model in the Unitary Gauge

Following systematically the generalized Hamiltonian approach of Batalin, Fradkin and Tyutin (BFT), we embed the second-class non-abelian SU(2) Higgs model in the unitary gauge into a gauge invariant theory. The strongly involutive Hamiltonian and constraints are obtained as an infinite power series in the auxiliary fields. Furthermore, comparing these results with those obtained from the gauged second class Lagrangian, we arrive at a simple interpretation for the first class Hamiltonian, constraints and observables.Comment: 13 pages, Latex, no figure

Strong enhancement of drag and dissipation at the weak- to strong- coupling phase transition in a bi-layer system at a total Landau level filling nu=1

We consider a bi-layer electronic system at a total Landau level filling factor nu =1, and focus on the transition from the regime of weak inter-layer coupling to that of the strongly coupled (1,1,1) phase (or ''quantum Hall ferromagnet''). Making the assumption that in the transition region the system is made of puddles of the (1,1,1) phase embedded in a bulk of the weakly coupled state, we show that the transition is accompanied by a strong increase in longitudinal Coulomb drag, that reaches a maximum of approximately $h/2e^{2}$. In that regime the longitudinal drag is increased with decreasing temperature.Comment: four pages, one included figur

VALIDATION OF OPTIMALLY DESIGNED STATOR-PROPELLER SYSTEM BY EFD AND CFD

The development of energy-saving devices to lower the energy efficiency design index (EEDI) of ships has been actively researched worldwide. One such device is an asymmetric pre-swirl stator, which helps to improve the propulsion efficiency by recovering the rotational energy generated during propeller rotation. Determining the pitch angle is the most important factor in the design of an efficient asymmetric pre-swirl stator. To optimize the pitch angle of an asymmetric pre-swirl stator, this study deals with potential-flow, computational fluid dynamics, and model tests. The model delivered power at a design speed of 24 kt was compared by changing the pitch angle by ±2° with respect to the reference angle designed using a potential-flow program. The commercial code Star-CCM+ was used for the numerical analysis, and the model was also tested in a towing tank at Pusan National University. This study proposes an effective method for determining and verifying the optimal pitch angle of an asymmetric pre-swirl stator