Operation of Faddeev-Kernel in Configuration Space

We present a practical method to solve Faddeev three-body equations at energies above three-body breakup threshold as integral equations in coordinate space. This is an extension of previously used method for bound states and scattering states below three-body breakup threshold energy. We show that breakup components in three-body reactions produce long-range effects on Faddeev integral kernels in coordinate space, and propose numerical procedures to treat these effects. Using these techniques, we solve Faddeev equations for neutron-deuteron scattering to compare with benchmark solutions.Comment: 20 pages, 8 figures, to be published in Few-Body System

Anisotropy, disorder, and superconductivity in CeCu2Si2 under high pressure

Resistivity measurements were carried out up to 8 GPa on single crystal and polycrystalline samples of CeCu2Si2 from differing sources in the homogeneity range. The anisotropic response to current direction and small uniaxial stresses was explored, taking advantage of the quasi-hydrostatic environment of the Bridgman anvil cell. It was found that both the superconducting transition temperature Tc and the normal state properties are very sensitive to uniaxial stress, which leads to a shift of the valence instability pressure Pv and a small but significant change in Tc for different orientations with respect to the tetragonal c-axis. Coexistence of superconductivity and residual resistivity close to the Ioffe-Regel limit around 5 GPa provides a compelling argument for the existence of a valence-fluctuation mediated pairing interaction at high pressure in CeCu2Si2.Comment: 12 pages, 7 figure

Controlled enhancement or suppression of exchange biasing using impurity δ\delta-layers

The effects of inserting impurity $\delta$-layers of various elements into a Co/IrMn exchange biased bilayer, at both the interface, and at given points within the IrMn layer a distance from the interface, has been investigated. Depending on the chemical species of dopant, and its position, we found that the exchange biasing can be either strongly enhanced or suppressed. We show that biasing is enhanced with a dusting of certain magnetic impurities, present at either at the interface or sufficiently far away from the Co/IrMn interface. This illustrates that the final spin structure at the Co/IrMn interface is not only governed by interface structure/roughness but is also mediated by local exchange or anisotropy variations within the bulk of the IrMn

The quantum phase transition of itinerant helimagnets

We investigate the quantum phase transition of itinerant electrons from a paramagnet to a state which displays long-period helical structures due to a Dzyaloshinskii instability of the ferromagnetic state. In particular, we study how the self-generated effective long-range interaction recently identified in itinerant quantum ferromagnets is cut-off by the helical ordering. We find that for a sufficiently strong Dzyaloshinskii instability the helimagnetic quantum phase transition is of second order with mean-field exponents. In contrast, for a weak Dzyaloshinskii instability the transition is analogous to that in itinerant quantum ferromagnets, i.e. it is of first order, as has been observed in MnSi.Comment: 5 pages RevTe

Integer Quantum Hall Effect with Realistic Boundary Condition : Exact Quantization and Breakdown

A theory of integer quantum Hall effect(QHE) in realistic systems based on von Neumann lattice is presented. We show that the momentum representation is quite useful and that the quantum Hall regime(QHR), which is defined by the propagator in the momentum representation, is realized. In QHR, the Hall conductance is given by a topological invariant of the momentum space and is quantized exactly. The edge states do not modify the value and topological property of $\sigma_{xy}$ in QHR. We next compute distribution of current based on effective action and find a finite amount of current in the bulk and the edge, generally. Due to the Hall electric field in the bulk, breakdown of the QHE occurs. The critical electric field of the breakdown is proportional to $B^{3/2}$ and the proportional constant has no dependence on Landau levels in our theory, in agreement with the recent experiments.Comment: 48 pages, figures not included, some additions and revision

The long-time dynamics of two hydrodynamically-coupled swimming cells

Swimming micro-organisms such as bacteria or spermatozoa are typically found in dense suspensions, and exhibit collective modes of locomotion qualitatively different from that displayed by isolated cells. In the dilute limit where fluid-mediated interactions can be treated rigorously, the long-time hydrodynamics of a collection of cells result from interactions with many other cells, and as such typically eludes an analytical approach. Here we consider the only case where such problem can be treated rigorously analytically, namely when the cells have spatially confined trajectories, such as the spermatozoa of some marine invertebrates. We consider two spherical cells swimming, when isolated, with arbitrary circular trajectories, and derive the long-time kinematics of their relative locomotion. We show that in the dilute limit where the cells are much further away than their size, and the size of their circular motion, a separation of time scale occurs between a fast (intrinsic) swimming time, and a slow time where hydrodynamic interactions lead to change in the relative position and orientation of the swimmers. We perform a multiple-scale analysis and derive the effective dynamical system - of dimension two - describing the long-time behavior of the pair of cells. We show that the system displays one type of equilibrium, and two types of rotational equilibrium, all of which are found to be unstable. A detailed mathematical analysis of the dynamical systems further allows us to show that only two cell-cell behaviors are possible in the limit of $t\to\infty$, either the cells are attracted to each other (possibly monotonically), or they are repelled (possibly monotonically as well), which we confirm with numerical computations

Lower bound for the ground state energy of the no-pair Hamiltonian

A lower bound for the ground state energy of a one particle relativistic Hamiltonian - sometimes called no-pair operator - is provided.Comment: 5 pages, 1 figure, 1 table, Latex2e (amssymb,amsmath,graphicx

Scalar K pi form factor and light quark masses

Recent experimental improvements on K-decay data allow for a precise extraction of the strangeness-changing scalar K pi form factor and the related strange scalar spectral function. On the basis of this scalar as well as the corresponding pseudoscalar spectral function, the strange quark mass is determined to be m_s(2 GeV) = 92 +- 9 MeV. Further taking into account chiral perturbation theory mass ratios, the light up and down quark masses turn out to be m_u(2 GeV) = 2.7 +- 0.4 MeV as well as m_d(2 GeV) = 4.8 +- 0.5 MeV. As a by-product, we also find a value for the Cabibbo angle |V_{us}| = 0.2236(29) and the ratio of meson decay constants F_K/F_\pi = 1.203(16). Performing a global average of the strange mass by including extractions from other channels as well as lattice QCD results yields m_s(2 GeV) = 94 +- 6 MeV.Comment: 5 pages, 2 figures; comparison with lattice and global average added; version to appear in Phys. Rev.

Continuous Transition between Antiferromagnetic Insulator and Paramagnetic Metal in the Pyrochlore Iridate Eu2Ir2O7

Our single crystal study of the magneto-thermal and transport properties of the pyrochlore iridate Eu2Ir2O7 reveals a continuous phase transition from a paramagnetic metal to an antiferromagnetic insulator for a sample with stoichiometry within ~1% resolution. The insulating phase has strong proximity to an antiferromagnetic semimetal, which is stabilized by several % level of the off-stoichiometry. Our observations suggest that in addition to electronic correlation and spin-orbit coupling the magnetic order is essential for opening the charge gap.Comment: 6 pages, 6 figure