Phonon dispersion and electron-phonon coupling in MgB_2 and AlB_2

We present a first principles investigation of the lattice dynamics and electron-phonon coupling of the superconductor MgB_2 and the isostructural AlB_2 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. Complete phonon dispersion curves and Eliashberg functions \alpha^2F are calculated for both systems. We also report on Raman measurements, which support the theoretical findings. The calculated generalized density-of-states for MgB_2 is in excellent agreement with recent neutron-scattering experiments. The main differences in the calculated phonon spectra and \alpha^2F are related to high frequency in-plane boron vibrations. As compared to AlB_2, they are strongly softened in MgB_2 and exhibit an exceptionally strong coupling to electronic states at the Fermi energy. The total coupling constants are \lambda_{MgB_2}=0.73 and \lambda_{AlB_2}=0.43. Implications for the superconducting transition temperature are briefly discussed.Comment: 10 pages, 4 figures, to appear in Phys. Rev. Let

Ab initio lattice dynamics and electron-phonon coupling of Bi(111)

We present a comprehensive ab initio study of structural, electronic, lattice dynamical and electron-phonon coupling properties of the Bi(111) surface within density functional perturbation theory. Relativistic corrections due to spin-orbit coupling are consistently taken into account. As calculations are carried out in a periodic slab geometry, special attention is given to the convergence with respect to the slab thickness. Although the electronic structure of Bi(111) thin films varies significantly with thickness, we found that the lattice dynamics of Bi(111) is quite robust and appears converged already for slabs as thin as 6 bilayers. Changes of interatomic couplings are confined mostly to the first two bilayers, resulting in super-bulk modes with frequencies higher than the optic bulk spectrum, and in an enhanced density of states at lower frequencies for atoms in the first bilayer. Electronic states of the surface band related to the outer part of the hole Fermi surfaces exhibit a moderate electron-phonon coupling of about 0.45, which is larger than the coupling constant of bulk Bi. States at the inner part of the hole surface as well as those forming the electron pocket close to the zone center show much increased couplings due to transitions into bulk projected states near Gamma_bar. For these cases, the state dependent Eliashberg functions exhibit pronounced peaks at low energy and strongly deviate in shape from a Debye-like spectrum, indicating that an extraction of the coupling strength from measured electronic self-energies based on this simple model is likely to fail.Comment: 30 pages, 11 figure

Strange semimetal dynamics in SrIrO3

The interplay of electronic correlations, multi-orbital excitations, and spin-orbit coupling is afertile ground for new states of matter in quantum materials. Here, we report on a polarizedRaman scattering study of semimetallic SrIrO3. The momentum-space selectivity of Ramanscattering allows to circumvent the challenge to resolve the dynamics of charges with verydifferent mobilities. The Raman responses of both holes and electrons display an electroniccontinuum extending far beyond the energies allowed in a regular Fermi liquid. Analyzing thisresponse within a memory function formalism, we extract their frequency dependent scat-tering rate and mass enhancement, from which we determine their DC-mobilities andelectrical resistivities that agree well with transport measurement. We demonstrate that itscharge dynamics is well described by a marginal Fermi liquid phenomenology, with a scat-tering rate close to the Planckian limit. This demonstrates the potential of this approach toinvestigate the charge dynamics in multi-band systems

Witnessing effective entanglement in a continuous variable prepare&measure setup and application to a QKD scheme using postselection

We report an experimental demonstration of effective entanglement in a prepare&measure type of quantum key distribution protocol. Coherent polarization states and heterodyne measurement to characterize the transmitted quantum states are used, thus enabling us to reconstruct directly their Q-function. By evaluating the excess noise of the states, we experimentally demonstrate that they fulfill a non-separability criterion previously presented by Rigas et al. [J. Rigas, O. G\"uhne, N. L\"utkenhaus, Phys. Rev. A 73, 012341 (2006)]. For a restricted eavesdropping scenario we predict key rates using postselection of the heterodyne measurement results.Comment: 12 pages, 12 figures, 2 table

Encouraging versatile thinking in algebra using the computer

In this article we formulate and analyse some of the obstacles to understanding the notion of a variable, and the use and meaning of algebraic notation, and report empirical evidence to support the hypothesis that an approach using the computer will be more successful in overcoming these obstacles. The computer approach is formulated within a wider framework ofversatile thinking in which global, holistic processing complements local, sequential processing. This is done through a combination of programming in BASIC, physical activities which simulate computer storage and manipulation of variables, and specific software which evaluates expressions in standard mathematical notation. The software is designed to enable the user to explore examples and non-examples of a concept, in this case equivalent and non-equivalent expressions. We call such a piece of software ageneric organizer because if offers examples and non-examples which may be seen not just in specific terms, but as typical, or generic, examples of the algebraic processes, assisting the pupil in the difficult task of abstracting the more general concept which they represent. Empirical evidence from several related studies shows that such an approach significantly improves the understanding of higher order concepts in algebra, and that any initial loss in manipulative facility through lack of practice is more than made up at a later stage

Relationship tensions and mood: Adult children’s daily experience of aging parents’ stubbornness

This study examined middle‐aged individuals’ reports of parents’ behaviors commonly attributed to stubbornness. Middle‐aged adults (N = 192) completed a 7‐day diary reporting their mood and how often they felt their parents (N = 254) engaged in behaviors often described as “stubbornness” (insistent or risky). Thirty‐one percent of middle‐aged children reported insistent behaviors, and 17% reported risky behaviors by their parent(s). Daily reports of parent behaviors attributed to stubbornness were positively associated with parent–child relationship quality, parent functional limitations, and child neuroticism. Reports of perceived parent insistent behaviors were also associated with greater daily negative mood among adult children. Findings highlight the impact of adult children’s daily perceptions of parent behaviors commonly attributed to stubbornness on the individual and relationship.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142899/1/pere12229_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142899/2/pere12229.pd