Non-vanishing Berry Phase in Chiral Insulators

The binary compounds FeSi, RuSi, and OsSi are chiral insulators crystallizing in the space group P2_13 which is cubic. By means of ab initio calculations we find for these compounds a non-vanishing electronic Berry phase, the sign of which depends on the handedness of the crystal. There is thus the possibility that the Berry phase signals the existence of a macroscopic electric polarization due to the electrons. We show that this is indeed so if a small external magnetic field is applied in the [111]-direction. The electric polarization is oscillatory in the magnetic field and possesses a signature that distinguishes the handedness of the crystal. Our findings add to the discussion of topological classifications of insulators and are significant for spintronics applications, and in particular, for a deeper understanding of skyrmions in insulators

Study of interacting electrons in graphene under the renormalized-ring-diagram approximation

Using the tight-binding model with long-range Coulomb interactions between electrons, we study some of the electronic properties of graphene. The Coulomb interactions are treated with the renormalized-ring-diagram approximation. By self-consistently solving the integral equations for the Green function, we calculate the spectral density. The obtained result is in agreement with experimental observation. In addition, we also compute the density of states, the distribution functions, and the ground-state energy. Within the present approximation, we find that the imaginary part of the self-energy fixed at the Fermi momentum varies as quadratic in energy close to the chemical potential, regardless the system is doped or not. This result appears to indicate that the electrons in graphene always behave like a moderately correlated Fermi liquid.Comment: 11 pages, 13 figure

New Born-Infeld and DpDp-Brane Actions under 2-Metric and 3-Metric Prescriptions

The parent action method is utilized to the Born-Infeld and $Dp$-brane theories. Various new forms of Born-Infeld and $Dp$-brane actions are derived by using this systematic approach, in which both the already known 2-metric and newly proposed 3-metric prescriptions are considered. An auxiliary worldvolume tensor field, denoted by ${\omega}_{{\mu}{\nu}}$, is introduced and treated probably as an additional worldvolume metric because it plays a similar role to that of the auxiliary worldvolume (also called {\em intrinsic}) metric ${\gamma}_{{\mu}{\nu}}$. Some properties, such as duality, permutation and Weyl invariance as a local worldvolume symmetry of the new forms are analyzed. In particular, a new symmetry, i.e. the double Weyl invariance is discovered in 3-metric forms.Comment: v1: 30 pages, 4 figures; v2: 31 pages, 4 figures, final version with some modifications to appear in Phys. Rev.

Equation of state for hard square lattice gases

A simple equation of state for a lattice gas of hard squares of side length $\lambda$ is presented. Comparing to the Monte Carlo simulations, the new equation of state is found to be quite accurate for the disordered fluid phase

Rotational Symmetry Breaking in Sodium Doped Cuprates

For reasonable parameters a hole bound to a Na^{+} acceptor in Ca_{2-x}Na_{x}CuO_{2}Cl_{2} has a doubly degenerate ground state whose components can be represented as states with even (odd) reflection symmetry around the x(y) -axes. The conductance pattern for one state is anisotropic as the tip of a tunneling microscope scans above the Cu-O-Cu bonds along the x(y)-axes. This anisotropy is pronounced at lower voltages but is reduced at higher voltages. Qualitative agreement with recent experiments leads us to propose this effect as an explanation of the broken local rotational symmetry.Comment: 10 pages, 4 figure

Heavy meson chiral perturbation theory in finite volume

We present the first step towards the estimation of finite volume effects in heavy-light meson systems using heavy meson chiral perturbation theory. We demonstrate that these effects can be amplified in both light-quark and heavy-quark mass extrapolations (interpolations) in lattice calculations. As an explicit example, we perform a one-loop calculation for the neutral B meson mixing system and show that finite volume effects, which can be comparable with currently quoted errors, are not negligible in both quenched and partially quenched QCD.Comment: Talk presented at Lattice2004(heavy), Fermilab, June 21st-26th, 2004. Three pages, two figure