68,666 research outputs found
Thermodynamics and the naked singularity in the Gamma-metric
We investigate a possible way of establishing a parallel between the third
law of black hole mechanics, and the strong version of the third law of
thermodynamics. We calculate the surface gravity and area for a naked singular
null surface in the Gamma-metric and explain in what sense this behaviour
violates thermodynamics
The Realization of Artificial Kondo Lattices in Nanostructured Arrays
The interplay of magnetic energies in a Kondo lattice is the underlying
physics of a heavy fermion system. Creating an artificial Kondo lattice system
by localizing the moments in an ordered metallic array provides a prototype
system to tune and study the energetic interplay while avoiding the
complications introduced by random alloying of the material. In this article,
we create a Kondo lattice system by fabricating a hexagonally ordered
nanostructured array using niobium as the host metal and cobalt as the magnetic
constituent. Electrical transport measurements and magnetoresistivity
measurements of these artificial lattices show that the competing exchange
coupling properties can be easily tuned by controlling the impurity percentage.
These artificial Kondo lattice systems enable the exploration of an artificial
superconductor which should lead to a deep understanding of the role of
magnetism in unconventional superconductors.Comment: Artificial Magnetic Crystal
Study of ground state phases for spin-1/2 Falicov-Kimball model on a triangular lattice
The spin-dependent Falicov-Kimball model (FKM) is studied on a triangular
lattice using numerical diagonalization technique and Monte-Carlo simulation
algorithm. Magnetic properties have been explored for different values of
parameters: on-site Coulomb correlation , exchange interaction and
filling of electrons. We have found that the ground state configurations
exhibit long range Ne\`el order, ferromagnetism or a mixture of both as is
varied. The magnetic moments of itinerant () and localized () electrons
are also studied. For the one-fourth filling case we found no magnetic moment
from - and -electrons for less than a critical value.Comment: 6 pages, 8 figure
Quantum mechanics without spacetime II : noncommutative geometry and the free point particle
In a recent paper we have suggested that a formulation of quantum mechanics
should exist, which does not require the concept of time, and that the
appropriate mathematical language for such a formulation is noncommutative
differential geometry. In the present paper we discuss this formulation for the
free point particle, by introducing a commutation relation for a set of
noncommuting coordinates. The sought for background independent quantum
mechanics is derived from this commutation relation for the coordinates. We
propose that the basic equations are invariant under automorphisms which map
one set of coordinates to another- this is a natural generalization of
diffeomorphism invariance when one makes a transition to noncommutative
geometry. The background independent description becomes equivalent to standard
quantum mechanics if a spacetime manifold exists, because of the proposed
automorphism invariance. The suggested basic equations also give a quantum
gravitational description of the free particle.Comment: 8 page
Feshbach resonances in ultracold 85Rb-87Rb and 6Li-87Rb mixtures
We present an analysis of experimentally accessible magnetic Feshbach
resonances in ultra-cold hetero-nuclear 85Rb-87Rb and 6Li-87Rb mixtures. Using
recent experimental measurements of the triplet scattering lengths for 6Li-87Rb
and 7Li-87Rb mixtures and Feshbach resonances for one combination of atomic
states, we create model potential curves and fine tune them to reproduce the
measured resonances and to predict the location of several experimentally
relevant resonances in Li-Rb collisions. To model 85Rb-87Rb collisions, we use
accurate Rb_2 potentials obtained previously from the analysis of experiments
on 87Rb-87Rb collisions. We find resonances that occur at very low magnetic
fields, below 10 G, which may be useful for entanglement generation in optical
lattices or atom chip magnetic traps.Comment: 8 pages, 5 figure
- …