Kondo effect in bosonic spin liquids

In a metal, a magnetic impurity is fully screened by the conduction electrons at low temperature. In contrast, impurity moments coupled to spin-1 bulk bosons, such as triplet excitations in paramagnets, are only partially screened, even at the bulk quantum critical point. We argue that this difference is not due to the quantum statistics of the host particles but instead related to the structure of the impurity-host coupling, by demonstrating that frustrated magnets with bosonic spinon excitations can display a bosonic version of the Kondo effect. However, the Bose statistics of the bulk implies distinct behavior, such as a weak-coupling impurity quantum phase transition, and perfect screening for a range of impurity spin values. We discuss implications of our results for the compound Cs2CuCl4, as well as possible extensions to multicomponent bosonic gases.     

Optical Storage in Side-Chain Liquid Crystalline Polyesters

Long-term, high resolution holographic storage has been achieved in side-chain liquid crystalline polyesters with high diffraction efficiency. The information can be completely erased by heating the film to about 80°C. The modular architecture of the polyesters permits a varition in the length of the main- and side-chains and the substituents of the azo chromophore. Each of these has a profound influence on the storage properties of the polyesters. In this article, we examine the influence of the length of the side-chains, the probe-beam-polarization dependence of the observed signal on the interface and the crystalline vs. amorphous nature of the films for optical storage.     

The More the Merrier?

The trade-off between traits in life-history strategies has been widely studied for sexual and parthenogenetic organisms, but relatively little is known about the reproduction strategies of asexual animals. Here, we investigate clonal reproduction in the freshwater planarian Schmidtea mediterranea, an important model organism for regeneration and stem cell research. We find that these flatworms adopt a randomized reproduction strategy that comprises both asymmetric binary fission and fragmentation (generation of multiple offspring during a reproduction cycle). Fragmentation in planarians has primarily been regarded as an abnormal behavior in the past; using a large-scale experimental approach, we now show that about one third of the reproduction events in S. mediterranea are fragmentations, implying that fragmentation is part of their normal reproductive behavior. Our analysis further suggests that certain characteristic aspects of the reproduction statistics can be explained in terms of a maximum relative entropy principle.     

Hydrogen adsorption on metal surfaces

Extensive calculations of the ground state properties of hydrogen chemisorbed on transition metal surfaces are presented. The calculations are performed using the effective medium theory. The results for the chemisorption energies on all the 3d, 4d and 5d metals presented are in good agreement with experiment. The trends along a particular row are shown to be dominated by the degree of filling of the d band. The full adiabatic potential energy surface is presented for a number of experimentally interesting systems, including H/Ni(111), H/Ni(110), H/W(100) and H/W(110). Equilibrium sites, bond lengths, vibrational frequencies and surface diffusion energies are deduced and compared with experiment. Again, agreement is good. The surface and adsorbate parameters determining those observables are discussed. It is shown that a simple canonical relationship exists between the perpendicular vibrational frequency and the metal-hydrogen bond length. This formulation, which is not based on pair potentials, should be useful as a first estimate of bond lengths from measured vibrational data.     

Matter-wave interferometer for large molecules

We demonstrate a near-field Talbot-Lau interferometer for C70 fullerene molecules. Such interferometers are particularly suitable for larger masses. Using three free-standing gold gratings of 1 microm period and a transversally incoherent but velocity-selected molecular beam, we achieve an interference fringe visibility of 40% with high count rate. Both the high visibility and its velocity dependence are in good agreement with a quantum simulation that takes into account the van der Waals interaction of the molecules with the gratings and are in striking contrast to a classical moiré model.     

Effective temperature in driven vortex lattices with random pinning

We study numerically correlation and response functions in nonequilibrium driven vortex lattices with random pinning. From a generalized fluctuation-dissipation relation, we calculate an effective transverse temperature in the fluid moving phase. We find that the effective temperature decreases with increasing driving force and becomes equal to the equilibrium melting temperature when the dynamic transverse freezing occurs. We also discuss how the effective temperature can be measured experimentally from a generalized Kubo formula.     

Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics

The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations, the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width at the surface, in agreement with the STM observations. Implications for surface-induced cross slip are discussed.     

Anharmonic corrections for linear triatomic molecules subject to the Rennet-Teller effect

The effects of vibrational anharmonic terms and of the g_K -correction on the energy levels of a triatomic molecule in a degenerate electronic state are considered. The electronic wavefunctions are described using the approach first suggested in the original paper of Renner. Formulae for the anharmonic corrections in a number of different situations are derived. For an electronic Π state the corrections are given in the form where i runs over the various contributions and x ₁, x ₂, … depend on the anharmonic force constants. The functions F_i can be determined numerically (see equations (4.3) and 4.7)). For the case without spin-orbit interaction the F_i s are given explicitly to first order in ∈ in table 1. Further-more, the same results apply for levels with |K|=v ₂+1 even if the spinorbit interaction is not negligible. Explicit results for levels with |K|<v ₂ including spin-orbit interaction are given in tables 2 and 3. The cases with larger values for Λ (2, 3, …) are also considered. The energy level formulae for a Δ state differ from those derived earlier by Merer and Travis. In particular, the small separation between the vibronic Φ and Π levels with v ₂=1 is now found to be 4g_K . The additional terms that arise from end-over-end rotation of the molecule are discussed in § 6.