A Tunable Phonon-Exciton Fano System in Bilayer Graphene

Interference between different possible paths lies at the heart of quantum physics. Such interference between coupled discrete and continuum states of a system can profoundly change its interaction with light as seen in Fano resonance. Here we present a unique many-body Fano system composed of a discrete phonon vibration and continuous electron-hole pair transitions in bilayer graphene. Mediated by the electron-phonon interactions, the excited state is described by new quanta of elementary excitations of hybrid phonon-exciton nature. Infrared absorption of the hybrid states exhibit characteristic Fano lineshapes with parameters renormalized by many-body interactions. Remarkably, the Fano resonance in bilayer graphene is continuously tunable through electrical gating. Further control of the phonon-exciton coupling may be achieved with an optical field exploiting the excited state infrared activity. This tunable phonon-exciton system also offers the intriguing possibility of a 'phonon laser' with stimulated phonon amplification generated by population inversion of band-edge electrons.Comment: 21 pages, 3 figure

The Flagellum of Pseudomonas aeruginosa Is Required for Resistance to Clearance by Surfactant Protein A

Surfactant protein A (SP-A) is an important lung innate immune protein that kills microbial pathogens by opsonization and membrane permeabilization. We investigated the basis of SP-A-mediated pulmonary clearance of Pseudomonas aeruginosa using genetically-engineered SP-A mice and a library of signature-tagged P. aeruginosa mutants. A mutant with an insertion into flgE, the gene that encodes flagellar hook protein, was preferentially cleared by the SP-A(+/+) mice, but survived in the SP-A(-/-) mice. Opsonization by SP-A did not play a role in flgE clearance. However, exposure to SP-A directly permeabilized and killed the flgE mutant, but not the wild-type parental strain. P. aeruginosa strains with mutation in other flagellar genes, as well as mucoid, nonmotile isolates from cystic fibrosis patients, were also permeabilized by SP-A. Provision of the wild-type fliC gene restored the resistance to SP-A-mediated membrane permeabilization in the fliC-deficient bacteria. In addition, non-mucoid, motile revertants of CF isolates reacquired resistance to SP-A-mediated membrane permeability. Resistance to SP-A was dependent on the presence of an intact flagellar structure, and independent of flagellar-dependent motility. We provide evidence that flagellar-deficient mutants harbor inadequate amounts of LPS required to resist membrane permeabilization by SP-A and cellular lysis by detergent targeting bacterial outer membranes. Thus, the flagellum of P. aeruginosa plays an indirect but important role resisting SP-A-mediated clearance and membrane permeabilization

Higher Education Activities in World Cities: A Spatial Study of Global Leadership and Connectivity

Key characteristic of globalization is intensified interconnectedness among different places and individuals, beyond exchanges led by states and governments. However, existing literature on the geographies of higher education under globalization primarily focuses on the interactions at the regional scale and the intercountry level. Little is known about the disaggregate distribution of higher education activities in cities and the manner in which cities are connected in terms of academic linkages. This chapter reveals the spatial distribution of world cities with more higher education activities showing international standings and global connections. A four-indicator system of Globalizing Education Index, which consists of the Place Power and Network Power of cities, is proposed to measure the internationalization and connectivity of places. The spatial distribution of cities performing well in the four areas of prestigious-university standings, influential world scholars, international academic events, and global research networking suggests that decentralization of higher education activities is restricted to certain aspects, although the movement and information flows of the knowledge economy are supposedly more unrestricted under globalization. The geographical distribution of world cities with high Globalizing Education Index remains concentrated in North America with strong historical and cultural backgrounds of world academia and slightly spread to East Asia due to its strength in organizing international events. This chapter supplements existing geographical studies on higher education and proposes further research directions addressing the influence of geography and connectivity in facilitating academic activities with a global reach

Observation of three-dimensional massless Kane fermions in a zinc-blende crystal

http://arxiv.org/abs/1310.0969 The authors acknowledge helpful discussions with T. Brauner, R. Grill, M. Grynberg, A. A. Nersesyan, V. Novák, M. L. Sadowski and W. Zawadzki. The work has been supported by the ERC project MOMB, by EuroMagNET II under the EU Contract No. 228043, by the GDR-I project 'Semiconductor sources and detectors of THz frequencies' and by the Scientific Council of Montpellier II University. We also acknowledge the support received from the Ambassade de France en Russie for the French-Russian collaboration and exchange of PhD students.International audienceSolid-state physics and quantum electrodynamics, with its ultrarelativistic (massless) particles, meet in the electronic properties of one-dimensional carbon nanotubes, two-dimensional graphene or topological-insulator surfaces. However, clear experimental evidence for electronic states with a conical dispersion relation in all three dimensions, conceivable for certain bulk materials, is still missing. Here, we study a zinc-blende crystal, HgCdTe, at the point of the semiconductor-to-semimetal topological transition. For this compound, we observe three-dimensional massless electrons, as certified from the dynamical conductivity increasing linearly with the photon frequency, with a velocity of about 106 m s−1. Applying a magnetic field B results in a -dependence of dipole-active inter-Landau-level resonances and spin splitting of Landau levels also following a -dependence--well-established signatures of ultrarelativistic particles but until now not observed experimentally in any solid-state electronic system