4,566 research outputs found
Weak Mott insulators on the triangular lattice: possibility of a gapless nematic quantum spin liquid
We study the energetics of Gutzwiller projected BCS states of various
symmetries for the triangular lattice antiferromagnet with a four particle ring
exchange using variational Monte Carlo methods. In a range of parameters the
energetically favored state is found to be a projected paired
state which breaks lattice rotational symmetry. We show that the properties of
this nematic or orientationally ordered paired spin liquid state as a function
of temperature and pressure can account for many of the experiments on organic
materials. We also study the ring-exchange model with ferromagnetic Heisenberg
exchange and find that amongst the studied ans\"atze, a projected wave
state is the most favorable.Comment: Longer version, 7+ pages, 5 figure
Fermions in 3D Optical Lattices: Cooling Protocol to Obtain Antiferromagnetism
A major challenge in realizing antiferromagnetic (AF) and superfluid phases
in optical lattices is the ability to cool fermions. We determine the equation
of state for the 3D repulsive Fermi-Hubbard model as a function of the chemical
potential, temperature and repulsion using unbiased determinantal quantum Monte
Carlo methods, and we then use the local density approximation to model a
harmonic trap. We show that increasing repulsion leads to cooling, but only in
a trap, due to the redistribution of entropy from the center to the metallic
wings. Thus, even when the average entropy per particle is larger than that
required for antiferromagnetism in the homogeneous system, the trap enables the
formation of an AF Mott phase.Comment: 4 pages; 5 figures; also see supplementary material in 2 pages with 1
figur
Time Dependent Cosmologies and Their Duals
We construct a family of solutions in IIB supergravity theory. These are time
dependent or depend on a light-like coordinate and can be thought of as
deformations of AdS_5 x S^5. Several of the solutions have singularities. The
light-like solutions preserve 8 supersymmetries. We argue that these solutions
are dual to the N=4 gauge theory in a 3+1 dimensional spacetime with a metric
and a gauge coupling that is varying with time or the light-like direction
respectively. This identification allows us to map the question of singularity
resolution to the dual gauge theory.Comment: 13 pages REVTeX and AMSLaTeX. v2: corrected typos and made some
clarifications; reference added; v3: more clarifications, references adde
Gaussian Neighborhood-prime Labeling of Graphs Containing Hamiltonian Cycle
In this paper, we examine Gaussian neighborhood-prime labeling of generalized Peterson graph and graphs which contain Hamiltonian cycle
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Results of an aqueous source term model for a radiological risk assessment of the Drigg LLW Site, U.K.
A radionuclide source term model has been developed which simulates the biogeochemical evolution of the Drigg low level waste (LLW) disposal site. The DRINK (DRIgg Near field Kinetic) model provides data regarding radionuclide concentrations in groundwater over a period of 100,000 years, which are used as input to assessment calculations for a groundwater pathway. The DRINK model also provides input to human intrusion and gaseous assessment calculations through simulation of the solid radionuclide inventory. These calculations are being used to support the Drigg post closure safety case. The DRINK model considers the coupled interaction of the effects of fluid flow, microbiology, corrosion, chemical reaction, sorption and radioactive decay. It represents the first direct use of a mechanistic reaction-transport model in risk assessment calculations
Particle-Hole Symmetry and the Effect of Disorder on the Mott-Hubbard Insulator
Recent experiments have emphasized that our understanding of the interplay of
electron correlations and randomness in solids is still incomplete. We address
this important issue and demonstrate that particle-hole (ph) symmetry plays a
crucial role in determining the effects of disorder on the transport and
thermodynamic properties of the half-filled Hubbard Hamiltonian. We show that
the low-temperature conductivity decreases with increasing disorder when
ph-symmetry is preserved, and shows the opposite behavior, i.e. conductivity
increases with increasing disorder, when ph-symmetry is broken. The Mott
insulating gap is insensitive to weak disorder when there is ph-symmetry,
whereas in its absence the gap diminishes with increasing disorder.Comment: 4 pages, 4 figure
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