76,211 research outputs found
Higgs Searches at CMS and ATLAS
A summary of the sensitivity of the ATLAS and CMS experiments at the LHC to
discover a Standard Model Higgs boson is presented. Some prospects for Minimal
Supersymmetric Standard Model Higgs searches at LHC are also included.Comment: 4 pages, 6 figures, Proceedings for The XLIVth Rencontres de Moriond
session devoted to QCD AND HIGH ENERGY INTERACTIONS. 14-21st March 2009, La
Thuille, Ital
Equilibrium spin-glass transition of magnetic dipoles with random anisotropy axes on a site diluted lattice
We study partially occupied lattice systems of classical magnetic dipoles
which point along randomly oriented axes. Only dipolar interactions are taken
into account. The aim of the model is to mimic collective effects in disordered
assemblies of magnetic nanoparticles. From tempered Monte Carlo simulations, we
obtain the following equilibrium results. The zero temperature entropy
approximately vanishes. Below a temperature T_c, given by k_B T_c= (0.95 +-
0.1)x e_d, where e_d is a nearest neighbor dipole-dipole interaction energy and
x is the site occupancy rate, we find a spin glass phase. In it, (1) the mean
value , where q is the spin overlap, decreases algebraically with system
size N as N increases, and (2) D|q| = 0.5 (T/x)^1/2, independently of N,
where D|q| is the root mean square deviation of |q|.Comment: 7 LaTeX pages, 7 eps figures. Submitted to PRB on 30 December 200
Magnetism in graphene nano-islands
We study the magnetic properties of nanometer-sized graphene structures with
triangular and hexagonal shapes terminated by zig-zag edges. We discuss how the
shape of the island, the imbalance in the number of atoms belonging to the two
graphene sublattices, the existence of zero-energy states, and the total and
local magnetic moment are intimately related. We consider electronic
interactions both in a mean-field approximation of the one-orbital Hubbard
model and with density functional calculations. Both descriptions yield values
for the ground state total spin, , consistent with Lieb's theorem for
bipartite lattices. Triangles have a finite for all sizes whereas hexagons
have S=0 and develop local moments above a critical size of nm.Comment: Published versio
Higher-order supersymmetric quantum mechanics
We review the higher-order supersymmetric quantum mechanics (H-SUSY QM),
which involves differential intertwining operators of order greater than one.
The iterations of first-order SUSY transformations are used to derive in a
simple way the higher-order case. The second order technique is addressed
directly, and through this approach unexpected possibilities for designing
spectra are uncovered. The formalism is applied to the harmonic oscillator: the
corresponding H-SUSY partner Hamiltonians are ruled by polynomial Heisenberg
algebras which allow a straight construction of the coherent states.Comment: 42 pages, 12 eps figure
Noncollinear magnetic phases and edge states in graphene quantum Hall bars
Application of a perpendicular magnetic field to charge neutral graphene is
expected to result in a variety of broken symmetry phases, including
antiferromagnetic, canted and ferromagnetic. All these phases open a gap in
bulk but have very different edge states and non-collinear spin order, recently
confirmed experimentally. Here we provide an integrated description of both
edge and bulk for the various magnetic phases of graphene Hall bars making use
of a non-collinear mean field Hubbard model. Our calculations show that, at the
edges, the three types of magnetic order are either enhanced (zigzag) or
suppressed (armchair). Interestingly, we find that preformed local moments in
zigzag edges interact with the quantum Spin Hall like edge states of the
ferromagnetic phase and can induce back-scattering.Comment: 5 pages, 4 figure
Spin-transfer torque on a single magnetic adatom
We theoretically show how the spin orientation of a single magnetic adatom
can be controlled by spin polarized electrons in a scanning tunneling
microscope configuration. The underlying physical mechanism is spin assisted
inelastic tunneling. By changing the direction of the applied current, the
orientation of the magnetic adatom can be completely reversed on a time scale
that ranges from a few nanoseconds to microseconds, depending on bias and
temperature. The changes in the adatom magnetization direction are, in turn,
reflected in the tunneling conductance.Comment: 5 pages, 3 figure
SUSUSY quantum mechanics
The exactly solvable eigenproblems in Schr\"odinger quantum mechanics
typically involve the differential "shift operators". In the standard
supersymmetric (SUSY) case, the shift operator turns out to be of first order.
In this work, I discuss a technique to generate exactly solvable eigenproblems
by using second order shift operators. The links between this method and SUSY
are analysed. As an example, we show the existence of a two-parametric family
of exactly solvable Hamiltonians, which contains the Abraham-Moses potentials
as a particular case.Comment: 7 pages, 2 encapsulated postscript figures, uses epsf.sty talk given
at the II International Workshop on Classical and Quantum Integrable Systems,
Dubna (Russia), 8-12 July (1996) to be published in Int. J. Mod. Phys.
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