Competitions in layered ruthenates: ferro- vs. antiferromagnetism and triplet vs. singlet pairing

Ru based perovskites demonstrate an amazing richness in their magnetic properties, including 3D and quasi-2D ferromagnetism, antiferromagnetism, and unconventional superconductivity. Tendency to ferromagnetism, stemming from the unusually large involvement of O in magnetism in ruthenates, leads to ferromagnetic spin fluctuations in Sr2RuO4 and eventually to p-wave superconductivity. A related compound Ca2RuO4 was measured to be antiferromagnetic, suggesting a possibility of antiferromagnetic fluctuations in Sr2RuO4 as well. Here we report first principles calculations that demonstrate that in both compounds the ferro- and antiferromagnetic fluctuations coexist, leading to an actual instability in Ca2RuO4 and to a close competition between p-wave and d-wave superconducting symmetries in Sr2RuO4. The antiferromagnetism in this system appears to be mostly related with the nesting, which is the strongest at Q=(2pi/3,2pi/3,0). Surprisingly, for the Fermiology of Sr2RuO4 the p-wave state wins over the d-wave one everywhere except in close vicinity of the antiferromagnetic instability. The most stable state within the d-wave channel has vanishing order parameter at one out of three Fermi surfaces in Sr2RuO4, while in the p channel its amplitude is comparable at all three of them.Comment: 4 Revtex pages with 4 embedded postscript figure. Some figures are color, but should look OK in B&W as wel

Confined coherence in quasi-one-dimensional metals

We present a functional renormalization group calculation of the effect of strong interactions on the shape of the Fermi surface of weakly coupled metallic chains. In the regime where the bare interchain hopping is small, we show that scattering processes involving large momentum transfers perpendicular to the chains can completely destroy the warping of the true Fermi surface, leading to a confined state where the renormalized interchain hopping vanishes and a coherent motion perpendicular to the chains is impossible.Comment: 4 RevTex pages, 5 figures,final version as published by PR

Numerical investigation of the effects of pedestrian barriers on aeroelastic stability of a proposed footbridge

A numerical investigation into the aerodynamic characteristics and aeroelastic stability of a proposed footbridge across a motorway in the north of England has been undertaken. The longer than usual span, along with the unusual nature of the pedestrian barriers, indicated that the deck configuration was likely to be beyond the reliable limits of the British design code BD 49/01. In particular, the investigation focussed on the susceptibility of the bridge due to flutter, and to assess if the design wind speeds could be met satisfactorily. The calculations were performed using the discrete vortex method, DIVEX, developed at the Universities of Glasgow and Strathclyde. DIVEX has been successfully validated on a wide range of problems, including the aeroelastic response of bridge deck sections. The proposed deck configuration, which incorporated a pedestrian barrier comprised of angled flat plates, was found to be unstable at low wind speeds with the plates having a strong turning effect on the flow at the leading edge of the deck. DIVEX was used to assess a number of alternative design options, investigating the stability with respect to flutter for each configuration. Reducing the number of flat plates and their angle to the deck lessened the effect of the barrier on the overall aerodynamic characteristics and increased the stability of the bridge to an acceptable level, with the critical flutter speed in excess of the specified design speed

Renormalization group transformations on quantum states

We construct a general renormalization group transformation on quantum states, independent of any Hamiltonian dynamics of the system. We illustrate this procedure for translational invariant matrix product states in one dimension and show that product, GHZ, W and domain wall states are special cases of an emerging classification of the fixed points of this coarse--graining transformation.Comment: 5 pages, 2 figur

Radiative Correction to the Nuclear-Size Effect and Hydrogen-Deuterium Isotopic Shift

The radiative correction to the nuclear charge radius contribution to the Lamb shift of order $\alpha(Z\alpha)^5m_r^3$ is calculated. In view of the recent high precision experimental data, this theoretical correction produces a significant contribution to the hydrogen-deuterium isotopic shift.Comment: 5 pages, REVTEX, replaced with the final version, to be published in Phys.Rev. A, two references adde

Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling

We introduce and solve a semi-classical random walk (RW) model that describes the dynamics of spin polarization waves in zinc-blende semiconductor quantum wells. We derive the dispersion relations for these waves, including the Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the effects of an electric field applied parallel to the spin polarization wavevector. In agreement with fully quantum mechanical calculations [Kleinert and Bryksin, Phys. Rev. B \textbf{76}, 205326 (2007)], the RW approach predicts that spin waves acquire a phase velocity in the presence of the field that crosses zero at a nonzero wavevector, $q_0$. In addition, we show that the spin-wave decay rate is independent of field at $q_0$ but increases as $(q-q_0)^2$ for $q\neq q_0$. These predictions can be tested experimentally by suitable transient spin grating experiments