5,305 research outputs found
Dirac equation for quasi-particles in graphene and quantum field theory of their Coulomb interaction
There is evidence for existence of massless Dirac quasi-particles in
graphene, which satisfy Dirac equation in (1+2) dimensions near the so called
Dirac points which lie at the corners at the graphene's brilluoin zone. We
revisit the derivation of Dirac equation in (1+2) dimensions obeyed by
quasiparticles in graphene near the Dirac points. It is shown that parity
operator in (1+2) dimensions play an interesting role and can be used for
defining "conserved" currents resulting from the underlying Lagrangian for
Dirac quasi-particles in graphene which is shown to have U_{A}(1)*U_{B}(1)
symmetry. Further the quantum field theory (QFT) of Coulomb interaction of 2D
graphene is developed and applied to vacuum polarization and electron self
energy and the renormalization of the effective coupling g of this interaction
and Fermi velocity which has important implications in the
renormalization group analysis of g and v_{f}.Comment: 10 pages, some typos have been corrected, some references have been
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Spiral Spin Order and Transport Anisotropy in Underdoped Cuprates
We discuss the spiral spin density wave model and its application to explain
properties of underdoped LaSrCuO. We argue that the spiral
picture is theoretically well justified in the context of the extended
model, and then show that it can explain a number of observed features, such as
the location and symmetry of the incommensurate peaks in elastic neutron
scattering, as well as the in-plane resistivity anisotropy. A consistent
description of the low doping region (below 10% or so) emerges from the spiral
formulation, in which the holes show no tendency towards any type of charge
order and the physics is purely spin driven.Comment: 6 pages, 3 figures; Proceedings of the International Workshop on
Effective Models for Low-Dimensional Strongly Correlated Systems, September
2005, Peyresq, Franc
Thermodynamics of a gas of deconfined bosonic spinons in two dimensions
We consider the quantum phase transition between a Neel antiferromagnet and a
valence-bond solid (VBS) in a two-dimensional system of S=1/2 spins. Assuming
that the excitations of the critical ground state are linearly dispersing
deconfined spinons obeying Bose statistics, we derive expressions for the
specific heat and the magnetic susceptibility at low temperature T. Comparing
with quantum Monte Carlo results for the J-Q model, which is a candidate for a
deconfined Neel-VBS transition, we find excellent agreement, including a
previously noted logarithmic correction in the susceptibility. In our
treatment, this is a direct consequence of a confinement length scale Lambda
which is proportional to the correlation length xi raised to a non-trivial
power; Lambda ~ xi^(1+a) ~1/T^(1+a), with a>0 (with a approximately 0.2 in the
model).Comment: 4+ pages, 3 figures. v2: cosmetic changes onl
Study of shear viscosity of SU (2)-gluodynamics within lattice simulation
This paper is devoted to the study of two-point correlation function of the
energy-momentum tensor T_{12}T_{12} for SU(2)-gluodynamics within lattice
simulation of QCD. Using multilevel algorithm we carried out the measurement of
the correlation function at the temperature T/T_c = 1.2. It is shown that
lattice data can be described by spectral functions which interpolate between
hydrodynamics at low frequencies and asymptotic freedom at high frequencies.
The results of the study of spectral functions allowed us to estimate the ratio
of shear viscosity to the entropy density {\eta}/s = 0.134 +- 0.057.Comment: 7 pages, 3 figure
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