Plasmon losses due to electron-phonon scattering: the case of graphene encapsulated in hexagonal Boron Nitride

Graphene sheets encapsulated between hexagonal Boron Nitride (hBN) slabs display superb electronic properties due to very limited scattering from extrinsic disorder sources such as Coulomb impurities and corrugations. Such samples are therefore expected to be ideal platforms for highly-tunable low-loss plasmonics in a wide spectral range. In this Article we present a theory of collective electron density oscillations in a graphene sheet encapsulated between two hBN semi-infinite slabs (hBN/G/hBN). Graphene plasmons hybridize with hBN optical phonons forming hybrid plasmon-phonon (HPP) modes. We focus on scattering of these modes against graphene's acoustic phonons and hBN optical phonons, two sources of scattering that are expected to play a key role in hBN/G/hBN stacks. We find that at room temperature the scattering against graphene's acoustic phonons is the dominant limiting factor for hBN/G/hBN stacks, yielding theoretical inverse damping ratios of hybrid plasmon-phonon modes of the order of $50$-$60$, with a weak dependence on carrier density and a strong dependence on illumination frequency. We confirm that the plasmon lifetime is not directly correlated with the mobility: in fact, it can be anti-correlated.Comment: 14 pages, 4 figure

Deformation pattern in the underthrust carbonate-rich sequence of the Sibillini Thrust (central Italy): insights for shear zone evolution in modern subduction complexes

Modern convergent zones at tropical latitudes are characterized by subduction of carbonate sediment. Although carbonate response to deformation is different from clay, they are commonly treated as having a similar rheology. This approximation, though, is inadequate since carbonate behavior is complicated by cementation and pressure solution. Our goal, here, is to focus on the deformation of carbonate sediment in the footwall of a major fossil thrust zone and compare it with a possible scenario in a modern environment. The focus area is the Monti Sibillini Thrust, in the Umbria-Marche sector of the Northern Apennines where the pelagic, Late Eocene-Oligocene carbonates of the Scaglia Cinerea Formation are underthrusted beneath the late Cretaceous-Middle Eocene Scaglia Rossa Formation. The data collected during this meso-structural study allowed for an interpretation of the temporal and spatial relationships between the observed deformation structures (S-C deformation bands, shear veins and stylolites). Thes..

Plasmons and Coulomb drag in Dirac/Schroedinger hybrid electron systems

We show that the plasmon spectrum of an ordinary two-dimensional electron gas (2DEG) hosted in a GaAs heterostructure is significantly modified when a graphene sheet is placed on the surface of the semiconductor in close proximity to the 2DEG. Long-range Coulomb interactions between massive electrons and massless Dirac fermions lead to a new set of optical and acoustic intra-subband plasmons. Here we compute the dispersion of these coupled modes within the Random Phase Approximation, providing analytical expressions in the long-wavelength limit that shed light on their dependence on the Dirac velocity and Dirac-fermion density. We also evaluate the resistivity in a Coulomb-drag transport setup. These Dirac/Schroedinger hybrid electron systems are experimentally feasible and open new research opportunities for fundamental studies of electron-electron interaction effects in two spatial dimensions.Comment: 7 pages, 4 figure

Phylogenetic analysis of human rhinovirus isolates collected from otherwise healthy children with community-acquired pneumonia during five successive years

In order to evaluate the circulation of the different human rhinovirus (HRV) species and genotypes in Italian children with radiographically confirmed community-acquired pneumonia (CAP), a nasopharyngeal swab was obtained from 643 children admitted to hospital because of CAP during five consecutive winter and early spring seasons (2007-2012). Real-time reverse transcriptase polymerase chain reaction (RT-PCR) was used to identify HRV, and the HRV-positive samples were used for sequencing analysis and to reconstruct the phylogenetic tree. HRV was identified in 198 samples (42.2%), and the VP4/VP2 region was successfully amplified in 151 (76.3%). HRV-A was identified in 78 samples (51.6%), HRV-B in 14 (9.3%) and HRV-C in 59 (39.1%). Forty-seven (31.1%) of the children with HRV infection were aged <1 year, 71 (47.0%) were aged 1-3 years, and 33 (21.9%) were aged 654 years. Blast and phylogenetic analyses showed that the HRV strains were closely related to a total of 66 reference genotypes, corresponding to 29 HRV-A, 9 HRV-B and 28 HRV-C strains. Nucleotide variability was 37% between HRV-A and HRV-B, 37.3% between HRV-A and HRV-C, and 39.9% between HRV-B and HRV-C. A number of sequences clustered with known serotypes and, within these clusters, there were strains circulating during several seasons. The most frequently detected genotypes were HRV-A78 (n=17), HRV-A12 (n=9) and HRV-C2 (n=5). This study shows that, although it is mainly associated with HRV-A, pediatric CAP can also be diagnosed in subjects infected by HRV-C and, more rarely, by HRV-B. Moreover, a large number of genotypes may be involved in causing pediatric CAP and can be different from year to year. Although the prolonged circulation of the same genotypes can sometimes be associated with a number of CAP episodes in different years