Role of surface states in STM spectroscopy of (111) metal surfaces with Kondo adsorbates

A nearly-free-electron (NFE) model to describe STM spectroscopy of (111) metal surfaces with Kondo impurities is presented. Surface states are found to play an important role giving a larger contribution to the conductance in the case of Cu(111) and Au(111) than Ag(111) surfaces. This difference arises from the farther extension of the Ag(111) surface state into the substrate. The different line shapes observed when Co is adsorbed on different substrates can be explained from the position of the surface band onset relative to the Fermi energy. The lateral dependence of the line shape amplitude is found to be bulk-like for R|| < 4 Amstrongs and surface-like at larger distances, in agreement with experimental data.Comment: 4 pages, 3 eps figure

Spin-Orbit-Induced Kondo Size Effect in Thin Films with 5/2-spin Impurities

Recently, for spin $S=5/2$ impurities quite different size dependence of the Kondo contribution to the resistivity was found experimentally than for S=2. Therefore previous calculation about the effect of the spin-orbit-induced magnetic anisotropy on the Kondo amplitude of the resistivity is extended to the case of $S=5/2$ impurity spin which differs from the integer spin case as the ground state is degenerated. In this case the Kondo contribution remains finite when the sample size goes to zero and the thickness dependence in the Kondo resistivity is much weaker for Cu(Mn). The behavior of the Kondo coefficient as a function of the thickness depends on the Kondo temperature, that is somewhat stronger for larger $T_K$. Comparing our results with a recent experiment in thin Cu(Mn) films, we find a good agreement.Comment: 8 pages, ReVTeX + 4 figures (Postscript

Evidence for competition between the superconducting and the pseudogap state in (BiPb)_2(SrLa)_2CuO_{6+\delta} from muon-spin rotation experiments

The in-plane magnetic penetration depth \lambda_{ab} in optimally doped (BiPb)_2(SrLa)_2CuO_{6+\delta} (OP Bi2201) was studied by means of muon-spin rotation. The measurements of \lambda_{ab}^{-2}(T) are inconsistent with a simple model of a d-wave order parameter and a uniform quasiparticle weight around the Fermi surface. The data are well described assuming the angular gap symmetry obtained in ARPES experiments [Phys. Rev. Lett {\bf 98}, 267004 (2007)], where it was shown that the superconducting gap in OP Bi2201 exists only in segments of the Fermi surface near the nodes. We find that the remaining parts of the Fermi surface, which are strongly affected by the pseudogap state, do not contribute significantly to the superconducting condensate. Our data provide evidence that high temperature superconductivity and pseudogap behavior in cuprates are competing phenomena.Comment: 5 pages, 3 figure

A low-energy effective Yang-Mills theory for quark and gluon confinement

We derive a gauge-invariant low-energy effective model of the Yang-Mills theory. We find that the effective gluon propagator belongs to the Gribov-Stingl type and agrees with it when a mass term which breaks nilpotency of the BRST symmetry is included. We show that the effective model with gluon propagator of the Gribov-Stingl type exhibits both quark and gluon confinement: the Wilson loop average has the area law and the Schwinger function violates reflection positivity. However, we argue that both quark and gluon confinement can be obtained even in the absence of such a mass term.Comment: 5 pages, no figures; accepted for publication in Physical Review D (Rapid Communication

On ghost condensation, mass generation and Abelian dominance in the Maximal Abelian Gauge

Recent work claimed that the off-diagonal gluons (and ghosts) in pure Yang-Mills theories, with Maximal Abelian gauge fixing (MAG), attain a dynamical mass through an off-diagonal ghost condensate. This condensation takes place due to a quartic ghost interaction, unavoidably present in MAG for renormalizability purposes. The off-diagonal mass can be seen as evidence for Abelian dominance. We discuss why ghost condensation of the type discussed in those works cannot be the reason for the off-diagonal mass and Abelian dominance, since it results in a tachyonic mass. We also point out what the full mechanism behind the generation of a real mass might look like.Comment: 7 pages; uses revtex

Electrical control of spin dynamics in finite one-dimensional systems

We investigate the possibility of the electrical control of spin transfer in monoatomic chains incorporating spin-impurities. Our theoretical framework is the mixed quantum-classical (Ehrenfest) description of the spin dynamics, in the spirit of the s-d-model, where the itinerant electrons are described by a tight-binding model while localized spins are treated classically. Our main focus is on the dynamical exchange interaction between two well-separated spins. This can be quantified by the transfer of excitations in the form of transverse spin oscillations. We systematically study the effect of an electrostatic gate bias V_g on the interconnecting channel and we map out the long-range dynamical spin transfer as a function of V_g. We identify regions of V_g giving rise to significant amplification of the spin transmission at low frequencies and relate this to the electronic structure of the channel.Comment: 9 pages, 11 figure