Quasi-Particle Spectra, Charge-Density-Wave, Superconductivity and Electron-Phonon Coupling in 2H-NbSe2

High-resolution photoemission has been used to study the electronic structure of the charge density wave (CDW) and superconducting (SC) dichalcogenide, 2H- NbSe2. From the extracted self-energies, important components of the quasiparticle (QP) interactions have been identified. In contrast to previously studied TaSe2, the CDW transition does not affect the electronic properties significantly. The electron-phonon coupling is identified as a dominant contribution to the QP self-energy and is shown to be very anisotropic (k-dependent) and much stronger than in TaSe2.Comment: 4 pages, 3 figures, minor changes, to appear in PR

Static and Dynamic Phases for Vortex Matter with Attractive Interactions

Exotic vortex states with long range attraction and short range repulsion have recently been proposed to arise in superconducting hybrid structures and multi-band superconductors. Using large scale simulations we examine the static and dynamic properties of such vortex states interacting with random and periodic pinning. In the absence of pinning this system does not form patterns but instead completely phase separates. When pinning is present there is a transition from inhomogeneous to homogeneous vortex configurations similar to a wetting phenomenon. Under an applied drive, a dynamical dewetting process can occur from a strongly pinned homogeneous state into pattern forming states. We show that a signature of the exotic vortex interactions under transport measurements is a robust double peak feature in the differential conductivity curves.Comment: 5 pages, 4 postscript figure

A dynamical model of surrogate reactions

A new dynamical model is developed to describe the whole process of surrogate reactions; transfer of several nucleons at an initial stage, thermal equilibration of residues leading to washing out of shell effects and decay of populated compound nuclei are treated in a unified framework. Multi-dimensional Langevin equations are employed to describe time-evolution of collective coordinates with a time-dependent potential energy surface corresponding to different stages of surrogate reactions. The new model is capable of calculating spin distributions of the compound nuclei, one of the most important quantity in the surrogate technique. Furthermore, various observables of surrogate reactions can be calculated, e.g., energy and angular distribution of ejectile, and mass distributions of fission fragments. These features are important to assess validity of the proposed model itself, to understand mechanisms of the surrogate reactions and to determine unknown parameters of the model. It is found that spin distributions of compound nuclei produced in $^{18}$O+$^{238}$U $\rightarrow ^{16}$O+$^{240*}$U and $^{18}$O+$^{236}$U $\rightarrow ^{16}$O+$^{238*}$U reactions are equivalent and much less than 10$\hbar$, therefore satisfy conditions proposed by Chiba and Iwamoto (PRC 81, 044604(2010)) if they are used as a pair in the surrogate ratio method.Comment: 17 pages, 5 figure

Imaging characteristics and treatment of a penetrating brain injury caused by an oropharyngeal foreign body in a dog

A 4-year-old Border collie was presented with one episode of collapse, altered mentation, and a suspected pharyngeal stick injury. Magnetic resonance imaging (MRI) and computed tomography showed a linear foreign body penetrating the right oropharynx, through the foramen ovale and the brain parenchyma. The foreign body was surgically removed and medical treatment initiated. Complete resolution of clinical signs was noted at recheck 8 weeks later. Repeat MRI showed chronic secondary changes in the brain parenchyma. To the authors' knowledge, this is the first report of the advanced imaging findings and successful treatment of a penetrating oropharyngeal intracranial foreign body in a dog

Giant vortices, vortex rings and reentrant behavior in type-1.5 superconductors

We predict that in a bulk type-1.5 superconductor the competing magnetic responses of the two components of the order parameter can result in a vortex interaction that generates group-stabilized giant vortices and unusual vortex rings in the absence of any extrinsic pinning or confinement mechanism. We also find within the Ginzburg-Landau theory a rich phase diagram with successions of behaviors like type-1 -> type-1.5 -> type-2 -> type-1.5 as temperature decreases.Comment: 5 pages, 4 figure

Baryonic Bound State of Vortices in Multicomponent Superconductors

We construct a bound state of three 1/3-quantized Josephson coupled vortices in three-component superconductors with intrinsic Josephson couplings, which may be relevant with regard to iron-based superconductors. We find a Y-shaped junction of three domain walls connecting the three vortices, resembling the baryonic bound state of three quarks in QCD. The appearance of the Y-junction (but not a Delta-junction) implies that in both cases of superconductors and QCD, the bound state is described by a genuine three-body interaction (but not by the sum of two-body interactions). We also discuss a confinement/deconfinement phase transition.Comment: 11 pages, 3 figures, one section on confinement/deconfinement transition added, published versio

High--Energy Photon--Hadron Scattering in Holographic QCD

This article provides an in-depth look at hadron high energy scattering by using gravity dual descriptions of strongly coupled gauge theories. Just like deeply inelastic scattering (DIS) and deeply virtual Compton scattering (DVCS) serve as clean experimental probes into non-perturbative internal structure of hadrons, elastic scattering amplitude of a hadron and a (virtual) "photon" in gravity dual can be exploited as a theoretical probe. Since the scattering amplitude at sufficiently high energy (small Bjorken x) is dominated by parton contributions (= Pomeron contributions) even in strong coupling regime, there is a chance to learn a lesson for generalized parton distribution (GPD) by using gravity dual models. We begin with refining derivation of Brower-Polchinski-Strassler-Tan (BPST) Pomeron kernel in gravity dual, paying particular attention to the role played by complex spin variable j. The BPST Pomeron on warped spacetime consists of a Kaluza-Klein tower of 4D Pomerons with non-linear trajectories, and we clarify the relation between Pomeron couplings and Pomeron form factor. We emphasize that the saddle point value j^* of the scattering amplitude in the complex j-plane representation is a very important concept in understanding qualitative behavior of the scattering amplitude. The total Pomeron contribution to the scattering is decomposed into the saddle point contribution and at most a finite number of pole contributions, and when the pole contributions are absent (which we call saddle point phase), kinematical variable (q,x,t) dependence of ln (1/q) evolution and ln(1/x) evolution parameters gamma_eff. and lambda_eff. in DIS and t-slope parameter B of DVCS in HERA experiment are all reproduced qualitatively in gravity dual

Interacting coronae of two T Tauri stars: first observational evidence for solar-like helmet streamers

Context {The young binary system V773 Tau A exhibits a persistent radio flaring activity that gradually increases from a level of a few mJy at apoastron to more than 100 mJy at periastron. Interbinary collisions between very large (> 15 R) magnetic structures anchored on the two rotating stars of the system have been proposed to be the origin of these periodic radio flares. Magnetic structures extended over tens of stellar radii, that can also account for the observed fast decay of the radio flares, seem to correspond to the typical solar semi-open quite extended magnetic configurations called helmet streamers.} Aims {We aim to find direct observational evidence for the postulated, solar-like, coronal topologies.} Methods {We performed seven-consecutive-day VLBI observations at 8.4 GHz using an array consisting of the VLBA and the 100-m Effelsberg telescope.} Results {Two distintive structures appear in the radio images here presented. They happen to be associated with the primary and secondary stars of the V773 Tau A system. In one image (Fig.2-B) the two features are extended up to 18 R each and are nearly parallel revealing the presence of two interacting helmet streamers. One image (Fig.2-E) taken a few hours after a flare monitored by the 100-m Effelsberg telescope shows one elongated fading structure substantially rotated with respect to those seen in the B run. The same decay scenario is seen in Fig.2-G for the helmet streamer associated with the other star.} Conclusions {This is the very first direct evidence revealing that even if the flare origin is magnetic reconnection due to interbinary collision, both stars independently emit in the radio range with structures of their own. These structures are helmet streamers, observed for the first time in stars other than the Sun.}Comment: 7 pages, 3 figures, A&A in pres

Low-Temperature Specific Heat of an Extreme-Type-II Superconductor at High Magnetic Fields

We present a detailed study of the quasiparticle contribution to the low-temperature specific heat of an extreme type-II superconductor at high magnetic fields. Within a T-matrix approximation for the self-energies in the mixed state of a homogeneous superconductor, the electronic specific heat is a linear function of temperature with a linear-$T$ coefficient $\gamma_s(H)$ being a nonlinear function of magnetic field $H$. In the range of magnetic fields H\agt (0.15-0.2)H_{c2} where our theory is applicable, the calculated $\gamma_s(H)$ closely resembles the experimental data for the borocarbide superconductor YNi$_2$B$_2$C.Comment: 7 pages, 2 figures, to appear in Physical Review

Critical fluctuation conductivity in layered superconductors in strong electric field

The paraconductivity, originating from critical superconducting order-parameter fluctuations in the vicinity of the critical temperature in a layered superconductor is calculated in the frame of the self-consistent Hartree approximation, for an arbitrarily strong electric field and zero magnetic field. The paraconductivity diverges less steep towards the critical temperature in the Hartree approximation than in the Gaussian one and it shows a distinctly enhanced variation with the electric field. Our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations in high-temperature superconductors.Comment: 11 pages, 2 figures, to be published in Phys. Rev.