Maxwell-Chern-Simons Q-balls

We examine the energetics of $Q$-balls in Maxwell-Chern-Simons theory in two space dimensions. Whereas gauged $Q$-balls are unallowed in this dimension in the absence of a Chern-Simons term due to a divergent electromagnetic energy, the addition of a Chern-Simons term introduces a gauge field mass and renders finite the otherwise-divergent electromagnetic energy of the $Q$-ball. Similar to the case of gauged $Q$-balls, Maxwell-Chern-Simons $Q$-balls have a maximal charge. The properties of these solitons are studied as a function of the parameters of the model considered, using a numerical technique known as relaxation. The results are compared to expectations based on qualitative arguments.Comment: 6 pages. Talk given at Theory CANADA 2, Perimeter Institut

Phase transitions in a gas of anyons

We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however now in the presence of a topological term added to the action corresponding to the total linking number between the loops. We compute the linking number using certain notions from knot theory. Adding the topological term converts the particles into anyons. Using the correspondence that the model is an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. We find the following new results. The system continues to exhibit a phase transition as a function of the anyon mass as it becomes small \cite{mnp}, although the phases do not change the manifestation of the symmetry. The Chern-Simons term has no effect on the Wilson loop, but it does affect the {\rm '}t Hooft loop. For a given configuration it adds the linking number of the 't Hooft loop with all of the dynamical vortex loops to the action. We find that both the Wilson loop and the 't Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, which is unexpected.Comment: 6 pages, 5 figure

Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4

It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity mediated by ferromagnetic fluctuations. So far neutron scattering experiments have failed to detect any clear evidence of ferromagnetic spin fluctuations but, instead, this type of experiments has been successful in confirming the existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this reason there have been many efforts to associate the contributions of such incommensurate fluctuations to the mechanism of its superconductivity. Our unpolarized inelastic neutron scattering measurements revealed that these incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some theoretical ideas that the incommensurate spin fluctuations with a c-axis anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR

f_K/f_pi in Full QCD with Domain Wall Valence Quarks

We compute the ratio of pseudoscalar decay constants f_K/f_pi using domain-wall valence quarks and rooted improved Kogut-Susskind sea quarks. By employing continuum chiral perturbation theory, we extract the Gasser-Leutwyler low-energy constant L_5, and extrapolate f_K/f_pi to the physical point. We find: f_K/f_pi = 1.218 (+- 0.002) (+0.011 -0.024) where the first error is statistical and the second error is an estimate of the systematic due to chiral extrapolation and fitting procedures. This value agrees within the uncertainties with the determination by the MILC collaboration, calculated using Kogut-Susskind valence quarks, indicating that systematic errors arising from the choice of lattice valence quark are small.Comment: 14 pages, 9 figure

The mean field infinite range p=3 spin glass: equilibrium landscape and correlation time scales

We investigate numerically the dynamical behavior of the mean field 3-spin spin glass model: we study equilibrium dynamics, and compute equilibrium time scales as a function of the system size V. We find that for increasing volumes the time scales $\tau$ increase like $\ln \tau \propto V$. We also present an accurate study of the equilibrium static properties of the system.Comment: 6 pages, 9 figure

Ginzburg-Landau Theory for a p-Wave Sr_2RuO_4 Superconductor: Vortex Core Structure and Extended London Theory

Based on a two dimensional odd-parity superconducting order parameter for Sr_2RuO_4 with p-wave symmetry, we investigate the single vortex and vortex lattice structure of the mixed phase near H_{c1}. Ginzburg-Landau calculations for a single vortex show a fourfold structure with an orientation depending on the microscopic Fermi surface properties. The corresponding extended London theory is developed to determine the vortex lattice structure and we find near H_{c1} a centered rectangular vortex lattice. As the field is increased from H_{c1} this lattice continuously deforms until a square vortex lattice is achieved. In the centered rectangular phase the field distribution, as measurable through \mu-SR experiments, exhibits a characteristic two peak structure (similar to that predicted in high temperature and borocarbide superconductors).Comment: 12 pages, 7 figure

Tunneling properties at the interface between superconducting Sr2RuO4 and a Ru micro-inclusion

We have investigated the magnetic field and temperature dependence of the tunneling spectra of the eutectic system Sr2RuO4-Ru. Electric contacts to individual Ru lamellae embedded in Sr2RuO4 enable the tunneling spectra at the interface between ruthenate and a Ru microinclusion to be measured. A zero bias conductance peak (ZBCP) was observed in the bias voltage dependence of the differential conductance, suggesting that Andreev bound states are present at the interface. The ZBCP starts to appear at a temperature well below the superconducting transition temperature. The onset magnetic field of the ZBCP is also considerably smaller than the upper critical field when the magnetic field is parallel to the ab-plane. We propose that the difference between the onset of the ZBCP and the onset of superconductivity can be understood in terms of the existence of the single-component state predicted by Sigrist and Monien.Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jpn. vol. 74 no.

Thermal conductivity in the vicinity of the quantum critical endpoint in Sr3Ru2O7

Thermal conductivity of Sr3Ru2O7 was measured down to 40 mK and at magnetic fields through the quantum critical endpoint at H_c = 7.85 T. A peak in the electrical resistivity as a function of field was mimicked by the thermal resistivity. In the limit as T -> 0 K we find that the Wiedemann-Franz law is satisfied to within 5% at all fields, implying that there is no breakdown of the electron despite the destruction of the Fermi liquid state at quantum criticality. A significant change in disorder (from $\rho_0$(H=0T) = 2.1 $\mu\Omega$ cm to 0.5 $\mu\Omega$ cm) does not influence our conclusions. At finite temperatures, the temperature dependence of the Lorenz number is consistent with ferromagnetic fluctuations causing the non-Fermi liquid behavior as one would expect at a metamagnetic quantum critical endpoint.Comment: 4 figures, published in PR

Cyclotron Resonance in the Layered Perovskite Superconductor Sr2RuO4

We have measured the cyclotron masses in Sr2RuO4 through the observation of periodic-orbit-resonances - a magnetic resonance technique closely related to cyclotron resonance. We obtain values for the alpha, beta and gamma Fermi surfaces of (4.33+/-0.05)me, (5.81+/-0.03)me and (9.71+/-0.11)me respectively. The appreciable differences between these results and those obtained from de Haas- van Alphen measurements are attributable to strong electron-electron interactions in this system. Our findings appear to be consistent with predictions for a strongly interacting Fermi liquid; indeed, semi-quantitative agreement is obtained for the electron pockets beta and gamma.Comment: 4 pages + 3 figure