9,431 research outputs found
Stacking dependence of carrier transport properties in multilayered black phosphorous
We present the effect of different stacking orders on carrier transport
properties of multi-layer black phosphorous. We consider three different
stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6
layers). We employ a hierarchical approach in density functional theory (DFT),
with structural simulations performed with Generalized Gradient Approximation
(GGA) and the bandstructure, carrier effective masses and optical properties
evaluated with the Meta-Generalized Gradient Approximation (MGGA). The carrier
transmission in the various black phosphorous sheets was carried out with the
non-equilibrium Greens function (NEGF) approach. The results show that ACA
stacking has the highest electron and hole transmission probabilities. The
results show tunability for a wide range of band-gap, carrier effective masses
and transmission with a great promise for lattice engineering (stacking order
and layers) in black phosphorous.Comment: 18 Pages , 10 figure
Entanglement production due to quench dynamics of an anisotropic XY chain in a transverse field
We compute concurrence and negativity as measures of two-site entanglement
generated by a power-law quench (characterized by a rate 1/tau and an exponent
alpha) which takes an anisotropic XY chain in a transverse field through a
quantum critical point (QCP). We show that only the even-neighbor pairs of
sites get entangled in such a process. Moreover, there is a critical rate of
quench, 1/tau_c, above which no two-site entanglement is generated; the entire
entanglement is multipartite. The ratio of the two-site entanglements between
consecutive even neighbors can be tuned by changing the quench rate. We also
show that for large tau, the concurrence (negativity) scales as sqrt{alpha/tau}
(alpha/tau), and we relate this scaling behavior to defect production by the
quench through a QCP.Comment: 5 pages including 4 figures; added a figure on multipartite
entanglement and some references -- this is the published versio
Probing Disordered Substrates by Imaging the Adsorbate in its Fluid Phase
Several recent imaging experiments access the equilibrium density profiles of
interacting particles confined to a two-dimensional substrate. When these
particles are in a fluid phase, we show that such data yields precise
information regarding substrate disorder as reflected in one-point functions
and two-point correlations of the fluid. Using Monte Carlo simulations and
replica generalizations of liquid state theories, we extract unusual two-point
correlations of time-averaged density inhomogeneities induced by disorder.
Distribution functions such as these have not hitherto been measured but should
be experimentally accessible.Comment: 10 pages revtex 4 figure
S-Matrix Formulation of Mesoscopic Systems and Evanescent Modes
The Landauer-Butikker formalism is an important formalism to study mesoscopic
systems. Its validity for linear transport is well established theoretically as
well as experimentally. Akkermans et al [Phys. Rev. Lett. {\bf 66}, 76 (1991)]
had shown that the formalism can be extended to study thermodynamic properties
like persistent currents. It was earlier verified for simple one dimensional
systems. We study this formula very carefully and conclude that it requires
reinterpretation in quasi one dimension. This is essentially because of the
presence of evanescent modes in quasi one dimension.Comment: non
Strong Coupling Theory for Interacting Lattice Models
We develop a strong coupling approach for a general lattice problem. We argue
that this strong coupling perspective represents the natural framework for a
generalization of the dynamical mean field theory (DMFT). The main result of
this analysis is twofold: 1) It provides the tools for a unified treatment of
any non-local contribution to the Hamiltonian. Within our scheme, non-local
terms such as hopping terms, spin-spin interactions, or non-local Coulomb
interactions are treated on equal footing. 2) By performing a detailed
strong-coupling analysis of a generalized lattice problem, we establish the
basis for possible clean and systematic extensions beyond DMFT. To this end, we
study the problem using three different perspectives. First, we develop a
generalized expansion around the atomic limit in terms of the coupling
constants for the non-local contributions to the Hamiltonian. By analyzing the
diagrammatics associated with this expansion, we establish the equations for a
generalized dynamical mean-field theory (G-DMFT). Second, we formulate the
theory in terms of a generalized strong coupling version of the Baym-Kadanoff
functional. Third, following Pairault, Senechal, and Tremblay, we present our
scheme in the language of a perturbation theory for canonical fermionic and
bosonic fields and we establish the interpretation of various strong coupling
quantities within a standard perturbative picture.Comment: Revised Version, 17 pages, 5 figure
Superfluid-insulator transitions of two-species Bosons in an optical lattice
We consider a realization of the two-species bosonic Hubbard model with
variable interspecies interaction and hopping strength. We analyze the
superfluid-insulator (SI) transition for the relevant parameter regimes and
compute the ground state phase diagram for odd filling at commensurate
densities. We find that in contrast to the even commensurate filling case, the
superfluid-insulator transition occurs with (a) simultaneous onset of
superfluidity of both species or (b) coexistence of Mott insulating state of
one species and superfluidity of the other or, in the case of unit filling, (c)
complete depopulation of one species. The superfluid-insulator transition can
be first order in a large region of the phase diagram. We develop a variational
mean-field method which takes into account the effect of second order quantum
fluctuations on the superfluid-insulator transition and corroborate the
mean-field phase diagram using a quantum Monte Carlo study.Comment: 12 pages, 11 figure
Quantum glass phases in the disordered Bose-Hubbard model
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal
disorder is determined using Quantum Monte Carlo simulations. A sequence of
quantum glass phases intervene at the interface between the Mott insulating and
the Superfluid phases of the clean system. In addition to the standard Bose
glass phase, the coexistence of gapless and gapped regions close to the Mott
insulating phase leads to a novel Mott glass regime which is incompressible yet
gapless. Numerical evidence for the properties of these phases is given in
terms of global (compressibility, superfluid stiffness) and local
(compressibility, momentum distribution) observables
- …