10,949 research outputs found
Simulating STM transport in alkanes from first principles
Simulations of scanning tunneling microscopy measurements for molecules on
surfaces are traditionally based on a perturbative approach, most typically
employing the Tersoff-Hamann method. This assumes that the STM tip is far from
the sample so that the two do not interact with each other. However, when the
tip gets close to the molecule to perform measurements, the electrostatic
interplay between the tip and substrate may generate non-trivial potential
distribution, charge transfer and forces, all of which may alter the electronic
and physical structure of the molecule. These effects are investigated with the
ab initio quantum transport code SMEAGOL, combining non-equilibrium Green's
functions formalism with density functional theory. In particular, we
investigate alkanethiol molecules terminated with either CH3 or CF3 end-groups
on gold surfaces, for which recent experimental data are available. We discuss
the effects connected to the interaction between the STM tip and the molecule,
as well as the asymmetric charge transfer between the molecule and the
electrodes.Comment: 10 pages, 18 figure
Meson correlators above deconfinement
We review recent progress in studying spectral functions for mesonic
observables at finite temperatures, by analysis of imaginary time correlators
directly calculated on isotropic lattices. Special attention is paid to the
lattice artifacts present in such calculations.Comment: Latex, 3 figures uses iopart.cls, talk presented at Hot Quarks 2004,
July 18-24, 2004, Taos Valley New Mexico, US
Origin of the 0.25-anomaly in the nonlinear conductance of a quantum point contact
We calculate the non-linear conductance of a quantum point contact using the
non-equilibrium Greens function technique within the Hartree approximation of
spinless electrons. We quantitative reproduce the 0.25-anomaly in the
differential conductance (i.e. the lowest plateau at 0.25-0.3*2e^2/h) as well
as an upward bending of higher conductance half-integer plateaus seen in the
experiments, and relate these features to the non-linear screening and pinning
effects.Comment: 6 pages, 4 figure
Partitioning technique for a discrete quantum system
We develop the partitioning technique for quantum discrete systems. The graph
consists of several subgraphs: a central graph and several branch graphs, with
each branch graph being rooted by an individual node on the central one. We
show that the effective Hamiltonian on the central graph can be constructed by
adding additional potentials on the branch-root nodes, which generates the same
result as does the the original Hamiltonian on the entire graph. Exactly
solvable models are presented to demonstrate the main points of this paper.Comment: 7 pages, 2 figure
Calculation of the Self-energy of Open Quantum Systems
We propose an easy method of calculating the self-energy of semi-infinite
leads attached to a mesoscopic system.Comment: 6 pages, 2 figures, published in J. Phys. Soc. Jp
Microwave stabilization of edge transport and zero-resistance states
Edge channels play a crucial role for electron transport in two dimensional
electron gas under magnetic field. It is usually thought that ballistic
transport along edges occurs only in the quantum regime with low filling
factors. We show that a microwave field can stabilize edge trajectories even in
the semiclassical regime leading to a vanishing longitudinal resistance. This
mechanism gives a clear physical interpretation for observed zero-resistance
states
Electronic Transport in Dual-gated Bilayer Graphene at Large Displacement Fields
We study the electronic transport properties of dual-gated bilayer graphene
devices. We focus on the regime of low temperatures and high electric
displacement fields, where we observe a clear exponential dependence of the
resistance as a function of displacement field and density, accompanied by a
strong non-linear behavior in the transport characteristics. The effective
transport gap is typically two orders of magnitude smaller than the optical
band gaps reported by infrared spectroscopy studies. Detailed temperature
dependence measurements shed light on the different transport mechanisms in
different temperature regimes.Comment: 4 pages, 3 figure
Charmonium at finite temperature
We study charmoinum correlators and spectral functions at finite temperature
within the quenched approximation using isotropic lattices with lattice spacing
a^-1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of
the ground state charmonium spectral function above deconfinement, we find that
ground state charmonia (J/psi and eta_c) exist in the deconfined phase at least
up to temperatures as high as 1.5Tc. P-wave charmonia (chi_c) on the other hand
are dissociated already at 1.12Tc.Comment: Contribution to Lattice 2003 (non-zero) LaTeX, 3 pages, 3 figures,
uses espcrc2 styl
Hadron correlators, spectral functions and thermal dilepton rates from lattice QCD
We discuss information on thermal modifications of hadron properties which
can be extracted from the structure of Euclidean correlation functions of
hadronic currents as well as more direct information obtained through the
reconstruction of the spectral functions based on the Maximum Entropy Method.Comment: 4 pages, latex2e, 5 EPS-files, invited contribution to the 16th Int.
Conf. on Ultra-Relativistic Nucleus-Nucleus Collisions, Nantes, France, 18 -
24 July, 200
Non-equilibrium spin polarization effects in spin-orbit coupling system and contacting metallic leads
We study theoretically the current-induced spin polarization effect in a
two-terminal mesoscopic structure which is composed of a semiconductor
two-dimensional electron gas (2DEG) bar with Rashba spin-orbit (SO) interaction
and two attached ideal leads. The nonequilibrium spin density is calculated by
solving the scattering wave functions explicitly within the ballistic transport
regime. We found that for a Rashba SO system the electrical current can induce
spin polarization in the SO system as well as in the ideal leads. The induced
polarization in the 2DEG shows some qualitative features of the intrinsic spin
Hall effect. On the other hand, the nonequilibrium spin density in the ideal
leads, after being averaged in the transversal direction, is independent of the
distance measured from the lead/SO system interface, except in the vicinity of
the interface. Such a lead polarization effect can even be enhanced by the
presence of weak impurity scattering in the SO system and may be detectable in
real experiments.Comment: 6 pages,5 figure
- …