86 research outputs found
Correlations, Plasmarons, and Quantum Spectral Function in Bilayer Graphene
We theoretically study the many-body effects of electron electron interaction
on the single particle spectral function of doped bilayer graphene. Using
random phase approximation, we calculate the real and imaginary part of the
self-energy and hence the spectral function. The spectral function near the
Fermi surface shows the usual quasiparticle peak, establishing doped bilayer
graphene, in contrast to the unstable neutral system, to be a Fermi liquid.
Away from the Fermi surface, an additional broad plasmaron peak is visible in
the spectral function. From the low energy behaviour of the self-energy we
calculate the quasiparticle residue and the effective mass of the
quasiparticles as a function of carrier density. We present results for both
the on-shell and the off-shell approximation for the quasiparticle
renormalization.Comment: 5 pages, 3 figure
Relative contributions of crust and mantle to the origin of the Bijli Rhyolite in a palaeoproterozoic bimodal volcanic sequence (Dongargarh group), central India
New mineralogical, bulk chemical and oxygen isotope data on the Palaeoproterozoic Bijli Rhyolite, the basal unit of a bimodal volcanic sequence (Dongargarh Group) in central India, and one of the most voluminous silicic volcanic expressions in the Indian Shield, are presented. The Bijli Rhyolite can be recognized as a poorly sorted pyroclastic deposit, and comprises of phenocrystic K-feldspar + albite ± anorthoclase set in fine-grained micro-fragmental matrix of quartz-feldspar-sericite-chlorite-iron-oxide ± calcite. The rocks are largely metaluminous with high SiO2, Na2O + K2O, Fe/Mg, Ga/Al, Zr, Ta, Sn, Y, REE and low CaO, Ba, Sr contents; the composition points to an 'A-type granite' melt. The rocks show negative Cs-, Sr-, Eu- and Ti- anomalies with incompatible element concentrations 2-3 times more than the upper continental crust (UCC). LREE is high (La/Yb ~20) and HREE 20-30 times chondritic. δ18Owhole-rock varies between 4.4 and 7.8‰ (mean 5.87±1.26‰). The Bijli melt is neither formed by fractionation of a basaltic magma, nor does it represent a fractionated crustal melt. It is shown that the mantle-derived high temperature basaltic komatiitic melts/high Mg basalts triggered crustal melting, and interacted predominantly with deep crust compositionally similar to the Average Archaean Granulite (AAG), and a shallower crustal component with low CaO and Al2O3 to give rise to the hybrid Bijli melts. Geochemical mass balance suggests that ~30% partial melting of AAG under anhydrous condition, instead of the upper continental crust (UCC) including the Amgaon granitoid gneiss reported from the area, better matches the trace element concentrations in the rocks. The similar Ta/Th of the rhyolites (0.060) and average granulite (0.065) vs. UCC (0.13) also support a deep crustal protolith. Variable contributions of crust and mantle, and action of hydrothermal fluid are attributed for the spread in δ18Owhole-rock values. The fast eruption of high temperature ~900°C) rhyolitic melts suggests a rapid drop in pressure of melting related to decompression in an extensional setting
Coulomb drag in monolayer and bilayer graphene
We theoretically calculate the interaction-induced frictional Coulomb drag
resistivity between two graphene monolayers as well as between two graphene
bilayers, which are spatially separated by a distance "". We show that the
drag resistivity between graphene monolayers can be significantly affected by
the intralayer momentum-relaxation mechanism. For energy independent intralayer
scattering, the frictional drag induced by inter-layer electron-electron
interaction goes asymptotically as and in the high-density () and low-density ()
limits, respectively. When long-range charge impurity scattering dominates
within the layer, the monolayer drag resistivity behaves as and for and ,
respectively. The density dependence of the bilayer drag is calculated to be
both in the large and small layer separation limit.
In the large layer separation limit, the bilayer drag has a strong
dependence on layer separation, whereas this goes to a weak logarithmic
dependence in the strong inter-layer correlation limit of small layer
separation. In addition to obtaining the asymptotic analytical formula for
Coulomb drag in graphene, we provide numerical results for arbitrary values of
density and layer separation interpolating smoothly between our asymptotic
theoretical results.Comment: 11 pages, 4 figures. Accepted for publication in Phys Rev B. This is
the longer version of arXiv:1105.3203 which it supersede
Preparation and detection of d-wave superfluidity in two-dimensional optical superlattices
We propose a controlled method to create and detect d-wave superfluidity with
ultracold fermionic atoms loaded in two-dimensional optical superlattices. Our
scheme consists in preparing an array of nearest-neighbor coupled square
plaquettes or ``superplaquettes'' and using them as building blocks to
construct a d-wave superfluid state. We describe how to use the coherent
dynamical evolution in such a system to experimentally probe the pairing
mechanism. We also derive the zero temperature phase diagram of the fermions in
a checkerboard lattice (many weakly coupled plaquettes) and show that by tuning
the inter-plaquette tunneling spin-dependently or varying the filling factor
one can drive the system into a d-wave superfluid phase or a Cooper pair
density wave phase. We discuss the use of noise correlation measurements to
experimentally probe these phases.Comment: 8 pages, 6 figure
Crossover from adiabatic to sudden interaction quenches in the Hubbard model: Prethermalization and nonequilibrium dynamics
The recent experimental implementation of condensed matter models in optical
lattices has motivated research on their nonequilibrium behavior. Predictions
on the dynamics of superconductors following a sudden quench of the pairing
interaction have been made based on the effective BCS Hamiltonian; however,
their experimental verification requires the preparation of a suitable excited
state of the Hubbard model along a twofold constraint: (i) a sufficiently
nonadiabatic ramping scheme is essential to excite the nonequilibrium dynamics,
and (ii) overheating beyond the critical temperature of superconductivity must
be avoided. For commonly discussed interaction ramps there is no clear
separation of the corresponding energy scales. Here we show that the matching
of both conditions is simplified by the intrinsic relaxation behavior of
ultracold fermionic systems: For the particular example of a linear ramp we
examine the transient regime of prethermalization [M. Moeckel and S. Kehrein,
Phys. Rev. Lett. 100, 175702 (2008)] under the crossover from sudden to
adiabatic switching using Keldysh perturbation theory. A real-time analysis of
the momentum distribution exhibits a temporal separation of an early energy
relaxation and its later thermalization by scattering events. For long but
finite ramping times this separation can be large. In the prethermalization
regime the momentum distribution resembles a zero temperature Fermi liquid as
the energy inserted by the ramp remains located in high energy modes. Thus
ultracold fermions prove robust to heating which simplifies the observation of
nonequilibrium BCS dynamics in optical lattices.Comment: 27 pages, 8 figures Second version with small modifications in
section
Spectrum of the Vortex Bound States of the Dirac and Schrodinger Hamiltonian in the presence of Superconducting Gaps
We investigate the vortex bound states both Schrodinger and Dirac Hamiltonian
with the s-wave superconducting pairing gap by solving the mean-field
Bogoliubov-de-Gennes equations. The exact vortex bound states spectrum is
numerically determined by the integration method, and also accompanied by the
quasi-classical analysis. It is found that the bound state energies is
proportional to the vortex angular momentum when the chemical potential is
large enough. By applying the external magnetic field, the vortex bound state
energies of the Dirac Hamiltonian are almost unchanged; whereas the energy
shift of the Schrodinger Hamiltonian is proportional to the magnetic field.
These qualitative differences may serve as an indirect evidence of the
existence of Majorana fermions in which the zero mode exists in the case of the
Dirac Hamiltonian only.Comment: 8 pages, 9 figure
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