Proximity Eliashberg theory of electrostatic field-effect-doping in superconducting films

We calculate the effect of a static electric field on the critical temperature of a s-wave one band superconductor in the framework of proximity effect Eliashberg theory. In the weak electrostatic field limit the theory has no free parameters while, in general, the only free parameter is the thickness of the surface layer where the electric field acts. We conclude that the best situation for increasing the critical temperature is to have a very thin film of a superconducting material with a strong increase of electron-phonon (boson) constant upon charging.Comment: 9 pages, 5 figure

Pressure effects on crystal and electronic structure of bismuth tellurohalides

We study the possibility of pressure-induced transitions from a normal semiconductor to a topological insulator (TI) in bismuth tellurohalides using density functional theory and tight-binding method. In BiTeI this transition is realized through the formation of an intermediate phase, a Weyl semimetal, that leads to modification of surface state dispersions. In the topologically trivial phase, the surface states exhibit a Bychkov-Rashba type dispersion. The Weyl semimetal phase exists in a narrow pressure interval of 0.2 GPa. After the Weyl semimetal--TI transition occurs, the surface electronic structure is characterized by gapless states with linear dispersion. The peculiarities of the surface states modification under pressure depend on the band-bending effect. We have also calculated the frequencies of Raman active modes for BiTeI in the proposed high-pressure crystal phases in order to compare them with available experimental data. Unlike BiTeI, in BiTeBr and BiTeCl the topological phase transition does not occur. In BiTeBr, the crystal structure changes with pressure but the phase remains a trivial one. However, the transition appears to be possible if the low-pressure crystal structure is retained. In BiTeCl under pressure, the topological phase does not appear up to 18 GPa due to a relatively large band gap width in this compound

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

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

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

DISSECTING THE MECHANISM OF NLRP3 INFLAMMASOME ACTIVATION IN INDIVIDUAL CELLS: THE ROLE OF REACTIVE OXYGEN SPECIES AND ORGANELLE DAMAGE

Inflammation underlies the pathology of numerous diseases. It can be initiated by macrophages through the secretion of pro-inflammatory cytokines, such as IL-18 and IL-1β, following the activation of a molecular complex called the inflammasome. Inflammasomes are a protein scaffolding complex consisting of three known components: a sensory NLR, such as NLRP3, ASC, and caspase-1. The NLRP3 inflammasome is activated by a diverse array of stimuli, including crystals, ATP, pore-forming toxins, such as tetanolysin O (TLO), and the potassium ionophore nigericin. Here, we have explored the mechanism of NLRP3 inflammasome activation using nigericin, TLO and ATP. We found that nigericin induced NLRP3 inflammasome activation in bone-marrow derived macrophages (BMDM) results in inflammasome dependent lysosomal membrane permeabilization (LMP), mitochondrial membrane permeabilization (MMP), and the processing and secretion of IL-1β. All of these events required mitochondrial reactive oxygen species (ROS). Through combining bulk biochemical assays with live cell analysis of individual cells, we provide a kinetic analysis and sequence of events resulting from nigericin stimulation of LPS primed BMDM. We recapitulated NLRP3 inflammasome activation in a dendritic cell line, using the novel system of D2SC-1 transduced with ASC. These transduced cells undergo a similar sequence of events as macrophages, confirming that this mechanism is a general result of NLRP3 inflammasome activation applicable to multiple cell types. Furthermore, we have found that ATP and TLO stimulation of BMDM results in a similar sequence of NLRP3 dependent events. ATP, but not nigericin, requires P2X7 for activation of the NLRP3 inflammasome. Surprisingly, inhibition of P2X4 blocked nigericin, but not ATP, induced, NLRP3-dependent IL-1β secretion in BMDM. Our work has demonstrated a central, common role for mitochondrial ROS in NLRP3 inflammasome activation and determined the kinetics of organelle crosstalk during inflammasome activation. These data place both the mitochondria and lysosomes in a critical position controlling NLRP3 inflammasome activation. Based on these results, we suggest mitochondrial ROS as a potential therapeutic target for treating NLRP3 inflammasome related diseases. Inhibition or scavenging of mitochondrial ROS would not only prevent the pro-inflammatory effects of IL-1β secretion in these patients, but also NLRP3 dependent organelle damage and the resulting cell death

Linear Response Calculations of Lattice Dynamics in Strongly Correlated Systems

We introduce a new linear response method to study the lattice dynamics of materials with strong correlations. It is based on a combination of dynamical mean field theory of strongly correlated electrons and the local density functional theory of electronic structure of solids. We apply the method to study the phonon dispersions of a prototype Mott insulator NiO. Our results show overall much better agreement with experiment than the corresponding local density predictions.Comment: 4 pages, 2 figure

Electron–phonon coupling and superconductivity in a 2D Tl–Pb compound on Si(111)

Electron–phonon interaction in a single-layer Tl–Pb compound on Si(111) is investigated within the density-functional theory and linear-response approach in the mixed-basis pseudopotential representation. It is found that phonon-induced scattering of electrons at the Fermi level is primarily determined by surface electronic states responsible for bonding at the interface and by low-energy, predominantly shear-vertical vibrations of adatoms. The contribution of substrate-localized vibrations involved in the electron–phonon scattering turns out to be small. We have also estimated the superconducting transition temperature Tc by solving the linearized gap equation of the Eliashberg theory. An analysis of phonon-mediated transitions for a number of electronic states in the Tl–Pb surface bands showed that the strength of the coupling varies with the binding energy, increasing as it approaches the Fermi level, and significantly depends on the surface band to which the state belongs