526 research outputs found
Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures
We report on the exchange bias between antiferromagnetic and ferroelectric
hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode
(Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance
measurements are performed to monitor the presence of an exchange bias field.
When the heteroestructure is biased by an electric field, it turns out that the
exchange bias field is suppressed. We discuss the dependence of the observed
effect on the amplitude and polarity of the electric field. Particular
attention is devoted to the role of current leakage across the ferroelectric
layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special
issue on multiferroics
Two-Dimensional Supersymmetry: From SUSY Quantum Mechanics to Integrable Classical Models
Two known 2-dim SUSY quantum mechanical constructions - the direct
generalization of SUSY with first-order supercharges and Higher order SUSY with
second order supercharges - are combined for a class of 2-dim quantum models,
which {\it are not amenable} to separation of variables. The appropriate
classical limit of quantum systems allows us to construct SUSY-extensions of
original classical scalar Hamiltonians. Special emphasis is placed on the
symmetry properties of the models thus obtained - the explicit expressions of
quantum symmetry operators and of classical integrals of motion are given for
all (scalar and matrix) components of SUSY-extensions. Using Grassmanian
variables, the symmetry operators and classical integrals of motion are written
in a unique form for the whole Superhamiltonian. The links of the approach to
the classical Hamilton-Jacobi method for related "flipped" potentials are
established.Comment: 19 page
Point vortices and classical orthogonal polynomials
Stationary equilibria of point vortices with arbitrary choice of circulations
in a background flow are studied. Differential equations satisfied by
generating polynomials of vortex configurations are derived. It is shown that
these equations can be reduced to a single one. It is found that polynomials
that are Wronskians of classical orthogonal polynomials solve the latter
equation. As a consequence vortex equilibria at a certain choice of background
flows can be described with the help of Wronskians of classical orthogonal
polynomials.Comment: 20 pages, 12 figure
Adaptation of the Landau-Migdal Quasiparticle Pattern to Strongly Correlated Fermi Systems
A quasiparticle pattern advanced in Landau's first article on Fermi liquid
theory is adapted to elucidate the properties of a class of strongly correlated
Fermi systems characterized by a Lifshitz phase diagram featuring a quantum
critical point (QCP) where the density of states diverges. The necessary
condition for stability of the Landau Fermi Liquid state is shown to break down
in such systems, triggering a cascade of topological phase transitions that
lead, without symmetry violation, to states with multi-connected Fermi
surfaces. The end point of this evolution is found to be an exceptional state
whose spectrum of single-particle excitations exhibits a completely flat
portion at zero temperature. Analysis of the evolution of the temperature
dependence of the single-particle spectrum yields results that provide a
natural explanation of classical behavior of this class of Fermi systems in the
QCP region.Comment: 26 pages, 14 figures. Dedicated to 100th anniversary of A.B.Migdal
birthda
Point vortices and polynomials of the Sawada-Kotera and Kaup-Kupershmidt equations
Rational solutions and special polynomials associated with the generalized
K_2 hierarchy are studied. This hierarchy is related to the Sawada-Kotera and
Kaup-Kupershmidt equations and some other integrable partial differential
equations including the Fordy-Gibbons equation. Differential-difference
relations and differential equations satisfied by the polynomials are derived.
The relationship between these special polynomials and stationary
configurations of point vortices with circulations Gamma and -2Gamma is
established. Properties of the polynomials are studied. Differential-difference
relations enabling one to construct these polynomials explicitly are derived.
Algebraic relations satisfied by the roots of the polynomials are found.Comment: 23 pages, 8 figure
Search for composite and exotic fermions at LEP 2
A search for unstable heavy fermions with the DELPHI detector at LEP is
reported. Sequential and non-canonical leptons, as well as excited leptons and
quarks, are considered. The data analysed correspond to an integrated
luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV
and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172
GeV and 161 GeV. The search for pair-produced new leptons establishes 95%
confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2,
depending on the channel. The search for singly produced excited leptons and
quarks establishes upper limits on the ratio of the coupling of the excited
fermio
Search for charginos in e+e- interactions at sqrt(s) = 189 GeV
An update of the searches for charginos and gravitinos is presented, based on
a data sample corresponding to the 158 pb^{-1} recorded by the DELPHI detector
in 1998, at a centre-of-mass energy of 189 GeV. No evidence for a signal was
found. The lower mass limits are 4-5 GeV/c^2 higher than those obtained at a
centre-of-mass energy of 183 GeV. The (\mu,M_2) MSSM domain excluded by
combining the chargino searches with neutralino searches at the Z resonance
implies a limit on the mass of the lightest neutralino which, for a heavy
sneutrino, is constrained to be above 31.0 GeV/c^2 for tan(beta) \geq 1.Comment: 22 pages, 8 figure
Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP
Promptly decaying lightest neutralinos and long-lived staus are searched for
in the context of light gravitino scenarios. It is assumed that the stau is the
next to lightest supersymmetric particle (NLSP) and that the lightest
neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector
at centre-of-mass energies from 161 to 183 \GeV are analysed. No evidence of
the production of these particles is found. Hence, lower mass limits for both
kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is
found to be greater than 71.5 GeV/c^2. In the search for long-lived stau,
masses less than 70.0 to 77.5 \GeVcc are excluded for gravitino masses from 10
to 150 \eVcc . Combining this search with the searches for stable heavy leptons
and Minimal Supersymmetric Standard Model staus a lower limit of 68.5 \GeVcc
may be set for the stau mas
Hadronization properties of b quarks compared to light quarks in e+e- -> q qbar from 183 to 200 GeV
The DELPHI detector at LEP has collected 54 pb^{-1} of data at a
centre-of-mass energy around 183 GeV during 1997, 158 pb^{-1} around 189 GeV
during 1998, and 187 pb^{-1} between 192 and 200 GeV during 1999. These data
were used to measure the average charged particle multiplicity in e+e- -> b
bbar events, _{bb}, and the difference delta_{bl} between _{bb} and the
multiplicity, _{ll}, in generic light quark (u,d,s) events: delta_{bl}(183
GeV) = 4.55 +/- 1.31 (stat) +/- 0.73 (syst) delta_{bl}(189 GeV) = 4.43 +/- 0.85
(stat) +/- 0.61 (syst) delta_{bl}(200 GeV) = 3.39 +/- 0.89 (stat) +/- 1.01
(syst). This result is consistent with QCD predictions, while it is
inconsistent with calculations assuming that the multiplicity accompanying the
decay of a heavy quark is independent of the mass of the quark itself.Comment: 13 pages, 2 figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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