12,766 research outputs found
Chemical-potential flow equations for graphene with Coulomb interactions
We calculate the chemical potential dependence of the renormalized Fermi
velocity and static dielectric function for Dirac quasiparticles in graphene
nonperturbatively at finite temperature. By reinterpreting the chemical
potential as a flow parameter in the spirit of the functional renormalization
group (fRG) we obtain a set of flow equations, which describe the change of
these functions upon varying the chemical potential. In contrast to the fRG the
initial condition of the flow is nontrivial and has to be calculated
separately. Our results confirm that the charge carrier density dependence of
the Fermi velocity is negligible, validating the comparison of the fRG
calculation at zero density of Bauer et al., Phys. Rev. B 92, 121409 (2015)
with the experiment of Elias et al., Nat. Phys. 7, 701 (2011).Comment: 7 pages, 4 figure
Origin of the structural phase transition in Li7La3Zr2O12
Garnet-type Li7La3Zr2O12 (LLZO) is a solid electrolyte material with a
low-conductivity tetragonal and a high-conductivity cubic phase. Using
density-functional theory and variable cell shape molecular dynamics
simulations, we show that the tetragonal phase stability is dependent on a
simultaneous ordering of the Li ions on the Li sublattice and a
volume-preserving tetragonal distortion that relieves internal structural
strain. Supervalent doping introduces vacancies into the Li sublattice,
increasing the overall entropy and reducing the free energy gain from ordering,
eventually stabilizing the cubic phase. We show that the critical temperature
for cubic phase stability is lowered as Li vacancy concentration (dopant level)
is raised and that an activated hop of Li ions from one crystallographic site
to another always accompanies the transition. By identifying the relevant
mechanism and critical concentrations for achieving the high conductivity
phase, this work shows how targeted synthesis could be used to improve
electrolytic performance
Extrapolated High-Order Propagators for Path Integral Monte Carlo Simulations
We present a new class of high-order imaginary time propagators for
path-integral Monte Carlo simulations by subtracting lower order propagators.
By requiring all terms of the extrapolated propagator be sampled uniformly, the
subtraction only affects the potential part of the path integral. The
negligible violation of positivity of the resulting path integral at small time
steps has no discernable affect on the accuracy of our method. Thus in
principle arbitrarily high order algorithms can be devised for path-integral
Monte Carlo simulations. We verify this claim is by showing that fourth, sixth,
and eighth order convergence can indeed be achieved in solving for the ground
state of strongly interacting quantum many-body systems such as bulk liquid
He.Comment: 9 pages and 3 figures. Submitted to J. Chem. Phy
Flavors in an expanding plasma
We consider the effect of an expanding plasma on probe matter by determining
time-dependent D7 embeddings in the holographic dual of an expanding viscous
plasma. We calculate the chiral condensate and meson spectra including
contributions of viscosity. The chiral condensate essentially confirms the
expectation from the static black hole. For the meson spectra we propose a
scheme that is in agreement with the adiabatic approximation. New contributions
arise for the vector mesons at the order of the viscosity terms.Comment: 15 pages, 7 figures; v2: accepted for publ. in Phys. Rev. D; revised
mass definition agrees with adiabatic approximatio
SrCu(PO): A real material realization of the 1D nearest neighbor Heisenberg chain
We present evidence that crystalline Sr_2Cu(PO_4)_2 is a nearly perfect
one-dimensional (1D) spin-1/2 anti-ferromagnetic Heisenberg model (AHM) chain
compound with nearest neighbor only exchange. We undertake a broad theoretical
study of the magnetic properties of this compound using first principles (LDA,
LDA+U calculations), exact diagonalization and Bethe-ansatz methodologies to
decompose the individual magnetic contributions, quantify their effect, and fit
to experimental data. We calculate that the conditions of one-dimensionality
and short-ranged magnetic interactions are sufficiently fulfilled that Bethe's
analytical solution should be applicable, opening up the possibility to explore
effects beyond the infinite chain limit of the AHM Hamiltonian. We begin such
an exploration by examining some extrinsic effects such as impurities and
defects
Geometric approach to condensates in holographic QCD
An SU(Nf)xSU(Nf) Yang-Mills theory on an extra-dimensional interval is
considered, with appropriate symmetry-breaking boundary conditions on the IR
brane. UV-brane to UV-brane correlators at high energies are compared with the
OPE of two-point functions of QCD quark currents. Condensates correspond to
departure from AdS of the (different) metrics felt by vector and axial
combinations, away from the UV brane. Their effect on hadronic observables is
studied: the extracted condensates agree with the signs and orders of magnitude
expected from QCD.Comment: References added: published version plus misprints correction
Variabel-variabel yang Mempengaruhi Pindah Merek Simcard Berbasis Gsm (Kasus Pengguna Kartu Telepon Gsm di Kalangan Mahasiswa di Kota Jambi
Brand switching is the important indicator to determine consumer loyalty. In order toexamine the brand switching behavior there are four factors examined: price,promotion, product attributes, and distribution. Based on the regression statisticaltest, it is concluded that simultaneously price (X1), promotion (X2), product attributes(X3) and distribution (X4) affect significantly unto GSM card's brand switching. But,partially brand switching doesn't affected by price, product's attribute, anddistribution except by promotion. Hence it is recommended to implement relationshipmarketing program through promotion activities to keep customer from brandswitching behavior
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