299 research outputs found
Theory of self-induced back-action optical trapping in nanophotonic systems
Optical trapping is an indispensable tool in physics and the life sciences.
However, there is a clear trade off between the size of a particle to be
trapped, its spatial confinement, and the intensities required. This is due to
the decrease in optical response of smaller particles and the diffraction limit
that governs the spatial variation of optical fields. It is thus highly
desirable to find techniques that surpass these bounds. Recently, a number of
experiments using nanophotonic cavities have observed a qualitatively different
trapping mechanism described as "self-induced back-action trapping" (SIBA). In
these systems, the particle motion couples to the resonance frequency of the
cavity, which results in a strong interplay between the intra-cavity field
intensity and the forces exerted. Here, we provide a theoretical description
that for the first time captures the remarkable range of consequences. In
particular, we show that SIBA can be exploited to yield dynamic reshaping of
trap potentials, strongly sub-wavelength trap features, and significant
reduction of intensities seen by the particle, which should have important
implications for future trapping technologiesComment: 7 pages, 5 figure
Low-Temperature Permittivity of Insulating Perovskite Manganites
Measurements of the low-frequency (f<=100 kHz) permittivity and conductivity
at T<= 150 K are reported for La(1-x)Ca(x)MnO(3) (0<=x<=1) and
Ca(1-y)Sr(y)MnO(3) (0<=y<=0.75) having antiferromagnetic, insulating ground
states covering a broad range of Mn valencies from Mn(3+) to Mn(4+). Static
dielectric constants are determined from the low-T limiting behavior. With
increasing T, relaxation peaks associated with charge-carrier hopping are
observed in the real part of the permittivities and analyzed to determine
dopant binding energies. The data are consistent with a simple model of
hydrogenic impurity levels and imply effective masses m*/m_e~3 for the Mn(4+)
compounds. Particularly interesting is a large dielectric constant (~100)
associated with the C-type antiferromagnetic state near the composition
La(0.2)Ca(0.8)MnO(3).Comment: 6 pages, 8 figures, PRB in pres
Impurity Conduction and Magnetic Polarons in Antiferromagnetic Oxides
Low-temperature transport and magnetization measurements for the
antiferromagnets SrMnO(3) and CaMnO(3) identify an impurity band of mobile
states separated by energy E from electrons bound in Coulombic potentials. Very
weak electric fields are sufficient to excite bound electrons to the impurity
band, increasing the mobile carrier concentration by more than three orders of
magnitude. The data argue against the formation of self-trapped magnetic
polarons (MPs) predicted by theory, and rather imply that bound MPs become
stable only for kT<<E.Comment: 4 pp., 4 fig
Heat Conduction and Magnetic Phase Behavior in Electron-Doped Ca_{1-x} La_x MnO_3(0 <= x <= 0.2)
Measurements of thermal conductivity (kappa) vs temperature are reported for
a series of Ca_{1-x} La_x MnO_3(0 <= x <= 0.2) specimens. For the undoped
(x=0), G-type antiferromagnetic compound a large enhancement of kappa below the
Neel temperature (T_N ~ 125 K) indicates a strong coupling of heat-carrying
phonons to the spin system. This enhancement exhibits a nonmonotonic behavior
with increasing x and correlates remarkably well with the small ferromagnetic
component of the magnetization reported previously [Neumeier and Cohn, Phys.
Rev. B 61 14319 (2000).] Magnetoelastic polaron formation appears to underly
the behavior of kappa and the magnetization at x <= 0.02.Comment: submitted to PRB; 4 pp., 4 Fig.'s, RevTex
Inhomogeneous magnetism in La-doped CaMnO3. (I) Nanometric-scale spin clusters and long-range spin canting
Neutron measurements on Ca{1-x}La{x}MnO3 (0.00 <= x <= 0.20) reveal the
development of a liquid-like spatial distribution of magnetic droplets of
average size ~10 Angstroms, the concentration of which is proportional to x
(one cluster per ~60 doped electrons). In addition, a long-range ordered
ferromagnetic component is observed for ~0.05 < x < ~0.14. This component is
perpendicularly coupled to the simple G-type antiferromagnetic (G-AFM)
structure of the undoped compound, which is a signature of a G-AFM + FM
spin-canted state. The possible relationship between cluster formation and the
stabilization of a long-range spin-canting for intermediate doping is
discussed.Comment: Submitted to Physical Review
Coupling of phonons with orbital dynamics and magnetism in CuSb2O6
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOStrongly interacting phonons and orbital excitations are observed in the same energy range for CuSb2O6, unlocking a so-far unexplored type of electron-phonon interaction. An orbital wave at similar to 550 cm(-1) softens on warming and strongly interferes with a phonon at similar to 500 cm(-1), giving rise to a merged excitation of mixed character. An electronic continuum grows on warming to the orbital ordering temperature T-oo = 400 K, generating an important phonon decay channel. This direct and simultaneous observation of orbital and vibrational excitations reveals details of their combined dynamics. In addition, phonon frequency anomalies due to magnetic correlations are observed below similar to 150 K, much above the three-dimensional magnetic ordering temperature T-N(3D) = 8.5 K, confirming one-dimensional magnetic correlations along Cu-O-O-Cu linear chains in the paramagnetic state.971715FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO2012/04870-7Sem informaçãoSem informaçãoAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig
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