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