Collective modes and sound propagation in a p-wave superconductor: Sr2_2RuO4_4

There are five distinct collective modes in the recently discovered p-wave superconductor Sr$_2$RuO$_4$; phase and amplitude modes of the order parameter, clapping mode (real and imaginary), and spin wave. The first two modes also exist in the ordinary s-wave superconductors, while the clapping mode with the energy $\sqrt{2} \Delta(T)$ is unique to Sr$_2$RuO$_4$ and couples to the sound wave. Here we report a theoretical study of the sound propagation in a two dimensional p-wave superconductor. We identified the clapping mode and study its effects on the longitudinal and transverse sound velocities in the superconducting state. In contrast to the case of $^3$He, there is no resonance absorption associated with the collective mode, since in metals $\omega/(v_F |{\bf q}|) \ll 1$, where $v_F$ is the Fermi velocity, {\bf q} is the wave vector, and $\omega$ is the frequency of the sound wave. However, the velocity change in the collisionless limit gets modified by the contribution from the coupling to the clapping mode. We compute this contribution and comment on the visibility of the effect. In the diffusive limit, the contribution from the collective mode turns out to be negligible. The behaviors of the sound velocity change and the attenuation coefficient near $T_c$ in the diffusive limit are calculated and compared with the existing experimental data wherever it is possible. We also present the results for the attenuation coefficients in both of the collisionless and diffusive limits at finite temperatures.Comment: RevTex, 12 pages, 2 figures, Replaced by the published versio

Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates

The electronic nematic order characterized by broken rotational symmetry has been suggested to play an important role in the phase diagram of the high temperature cuprates. We study the interplay between the electronic nematic order and a spin density wave order in the presence of a magnetic field. We show that a cooperation of the nematicity and the magnetic field induces a finite coupling between the spin density wave and spin-triplet staggered flux orders. As a consequence of such a coupling, the magnon gap decreases as the magnetic field increases, and it eventually condenses beyond a critical magnetic field leading to a field-induced spin density wave order. Both commensurate and incommensurate orders are studied, and the experimental implications of our findings are discussed.Comment: 5 pages, 3 figure

Subwavelength localization and toroidal dipole moment of spoof surface plasmon polaritons

We experimentally and theoretically demonstrate subwavelength scale localization of spoof surface plasmon polaritons at a point defect in a two-dimensional groove metal array. An analytical expression for dispersion relation of spoof surface plasmon polaritons substantiates the existence of a band gap where a defect mode can be introduced. A waveguide coupling method allows us to excite localized spoof surface plasmon polariton modes and measure their resonance frequencies. Numerical calculations confirm that localized modes can have a very small modal volume and a high Q factor both of which are essential in enhancing light-matter interactions. Interestingly, we find that the localized spoof surface plasmon polariton has a significant toroidal dipole moment, which is responsible for the high Q factor, as well as an electric quadrupole moment. In addition, the dispersion properties of spoof surface plasmon polaritons are analyzed using a modal expansion method and numerical calculations

Electron-hole asymmetry in Co- and Mn-doped SrFe2As2

Phase diagram of electron and hole-doped SrFe2As2 single crystals is investigated using Co and Mn substitution at the Fe-sites. We found that the spin-density-wave state is suppressed by both dopants, but the superconducting phase appears only for Co (electron)-doping, not for Mn (hole)-doping. Absence of the superconductivity by Mn-doping is in sharp contrast to the hole-doped system with K-substitution at the Sr sites. Distinct structural change, in particular the increase of the Fe-As distance by Mn-doping is important to have a magnetic and semiconducting ground state as confirmed by first principles calculations. The absence of electron-hole symmetry in the Fe-site-doped SrFe2As2 suggests that the occurrence of high-Tc superconductivity is sensitive to the structural modification rather than the charge doping.Comment: 7 pages, 6 figure

Control moment gyro optimization study

Control moment gyro optimizatio

The Development of an Augmented Contrained Efficiency Framework for the Adoption of Electrionic Interorganizational Governance

Business-to-business electronic commerce provides new mechanisms for interorganizational exchange governance. This study contributes to the research of the adoption of interorganizational exchange governance by developing an augmented constrained-efficiency framework that summarizes the salient factors influencing organizational selection and adoption of electronic exchange governance. Drawing upon the literature on organizational and interorganizational governance design and adoption, the augmented constrained-efficiency framework posits that organizational selection and adoption of electronic interorganizational exchange governance are an efficiency pursuing process and also constrained by some critical forces. Internally, the constraints include organizational decision makers’ bounded rationality and organizational resources and capabilities. Externally, an organization’s institutional environments, its dependency relationship, contractual arrangements and relational norms developed with its business partners through physical transactions are important constraining forces. To demonstrate the usefulness of the augmented constrained-efficiency framework, the paper applies it to the analysis of two important modes of electronic interorganizational exchange governance, namely electronic hierarchy and electronic marketplace. By doing so, the paper sets foundations for future theory development and empirical study

Superfluid density and competing orders in d-wave superconductors

We derive expressions for the superfluid density $\rho_s$ in the low-temperature limit $T \to 0$ in d-wave superconductors, taking into account the presence of competing orders such as spin-density waves, $i d_{xy}$-pairing, etc. Recent experimental data for the thermal conductivity and for elastic neutron scattering in La$_{2-x}$Sr$_x$CuO$_4$ suggest there are magnetic field induced anomalies that can be interpreted in terms of competing orders. We consider the implications of these results for the superfluid density and show in the case of competing spin-density wave order that the usual Volovik-like $\sqrt{H}$ depletion of $\rho_s(H)$ is replaced by a slower dependence on applied magnetic field. We find that it is crucial to include the competing order parameter in the self-consistent equation for the impurity scattering rate.Comment: 17 pages, RevTeX4, 6 EPS figures; final version published in PR

Dispersive Gap Mode of Phonons in Anisotropic Superconductors

We estimate the effect of the superconducting gap anisotropy in the dispersive gap mode of phonons, which is observed by the neutron scattering on borocarbide superconductors. We numerically analyze the phonon spectrum considering the electron-phonon coupling, and examine contributions coming from the gap suppression and the sign change of the pairing function on the Fermi surface. When the sign of the pairing function is changed by the nesting translation, the gap mode does not appear. We also discuss the suppression of the phonon softening of the Kohn anomaly due to the onset of superconductivity. We demonstrate that observation of the gap dispersive mode is useful for sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp

Endovascular repair or open repair for ruptured abdominal aortic aneurysm: a Cochrane systematic review

OBJECTIVES: Emergency endovascular aneurysm repair (eEVAR) may improve outcomes for patients with ruptured abdominal aortic aneurysm (RAAA). The study aim was to compare the outcomes for eEVAR with conventional open surgical repair for the treatment of RAAA. SETTING: A systematic review of relevant publications was performed. Randomised controlled trials (RCTs) comparing eEVAR with open surgical repair for RAAA were included. PARTICIPANTS: 3 RCTs were included, with a total of 761 patients with RAAA. INTERVENTIONS: Meta-analysis was performed with fixed-effects models with ORs and 95% CIs for dichotomous data and mean differences with 95% CIs for continuous data. PRIMARY AND SECONDARY OUTCOME MEASURES: Primary outcome was short-term mortality. Secondary outcome measures included aneurysm-specific and general complication rates, quality of life and economic analysis. RESULTS: Overall risk of bias was low. There was no difference between the 2 interventions on 30-day (or in-hospital) mortality, OR 0.91 (95% CI 0.67 to 1.22; p=0.52). 30-day complications included myocardial infarction, stroke, composite cardiac complications, renal complications, severe bowel ischaemia, spinal cord ischaemia, reoperation, amputation and respiratory failure. Reporting was incomplete, and no robust conclusion was drawn. For complication outcomes that did include at least 2 studies in the meta-analysis, there was no clear evidence to support a difference between eEVAR and open repair. Longer term outcomes and cost per patient were evaluated in only a single study, thus precluding definite conclusions. CONCLUSIONS: Outcomes between eEVAR and open repair, specifically 30-day mortality, are similar. However, further high-quality trials are required, as the paucity of data currently limits the conclusions