37,822 research outputs found
Quantum Criticality and Incipient Phase Separation in the Thermodynamic Properties of the Hubbard Model
Transport measurements on the cuprates suggest the presence of a quantum
critical point hiding underneath the superconducting dome near optimal hole
doping. We provide numerical evidence in support of this scenario via a
dynamical cluster quantum Monte Carlo study of the extended two-dimensional
Hubbard model. Single particle quantities, such as the spectral function, the
quasiparticle weight and the entropy, display a crossover between two distinct
ground states: a Fermi liquid at low filling and a non-Fermi liquid with a
pseudogap at high filling. Both states are found to cross over to a marginal
Fermi-liquid state at higher temperatures. For finite next-nearest-neighbor
hopping t' we find a classical critical point at temperature T_c. This
classical critical point is found to be associated with a phase separation
transition between a compressible Mott gas and an incompressible Mott liquid
corresponding to the Fermi liquid and the pseudogap state, respectively. Since
the critical temperature T_c extrapolates to zero as t' vanishes, we conclude
that a quantum critical point connects the Fermi-liquid to the pseudogap
region, and that the marginal-Fermi-liquid behavior in its vicinity is the
analogous of the supercritical region in the liquid-gas transition.Comment: 18 pages, 9 figure
Dynamics of a Rigid Rod in a Glassy Medium
We present simulations of the motion of a single rigid rod in a disordered
static 2d-array of disk-like obstacles. The rotational, , and
center-of-mass translational, , diffusion constants are calculated
for a wide range of rod length and density of obstacles . It is found
that follows the behavior predicted by kinetic theory for a hard
disk with an effective radius . A dynamic crossover is observed in
for comparable to the typical distance between neighboring
obstacles . Using arguments from kinetic theory and reptation, we
rationalize the scaling laws, dynamic exponents, and prefactors observed for
. In analogy with the enhanced translational diffusion observed in
deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for
.Comment: 8 pages, 4 figures. Major changes. To be published in Europhysics
Letter
String solutions in Chern-Simons-Higgs model coupled to an axion
We study a d=2+1 dimensional Chern-Simons gauge theory coupled to a Higgs
scalar and an axion field, finding the form of the potential that allows the
existence of selfdual equations and the corresponding Bogomolny bound for the
energy of static configurations. We show that the same conditions allow for the
N=2 supersymmetric extension of the model, reobtaining the BPS equations from
the supersymmetry requirement. Explicit electrically charged vortex-like
solutions to these equations are presented.Comment: 11 pages, 3 figure
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