69,441 research outputs found
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 -Brane Actions under 2-Metric and 3-Metric Prescriptions
The parent action method is utilized to the Born-Infeld and -brane
theories. Various new forms of Born-Infeld and -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 , 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
. 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
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
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