11,037 research outputs found
Strain-induced insulator state in La_0.7Sr_0.3CoO_3
We report on the observation of a strain-induced insulator state in
ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to
enhance the resistivity by several orders of magnitude. Reversible strain of
0.15% applied using a piezoelectric substrate triggers huge resistance
modulations, including a change by a factor of 10 in the paramagnetic regime at
300 K. However, below the ferromagnetic ordering temperature, the magnetization
data indicate weak dependence on strain for the spin state of the Co ions. We
interpret the changes observed in the transport properties in terms of a
strain-induced splitting of the Co e_g levels and reduced double exchange,
combined with a percolation-type conduction in an electronic cluster state
Reversible strain effect on the magnetization of LaCoO3 films
The magnetization of ferromagnetic LaCoO3 films grown epitaxially on
piezoelectric substrates has been found to systematically decrease with the
reduction of tensile strain. The magnetization change induced by the reversible
strain variation reveals an increase of the Co magnetic moment with tensile
strain. The biaxial strain dependence of the Curie temperature is estimated to
be below 4K/% in the as-grown tensile strain state of our films. This is in
agreement with results from statically strained films on various substrates
An atomic clock with instability
Atomic clocks have been transformational in science and technology, leading
to innovations such as global positioning, advanced communications, and tests
of fundamental constant variation. Next-generation optical atomic clocks can
extend the capability of these timekeepers, where researchers have long aspired
toward measurement precision at 1 part in . This milestone will
enable a second revolution of new timing applications such as relativistic
geodesy, enhanced Earth- and space-based navigation and telescopy, and new
tests on physics beyond the Standard Model. Here, we describe the development
and operation of two optical lattice clocks, both utilizing spin-polarized,
ultracold atomic ytterbium. A measurement comparing these systems demonstrates
an unprecedented atomic clock instability of after
only hours of averaging
Anomalous electronic Raman scattering in Na_xCoO_2 H_2O
Raman scattering experiments on Na_{x}CoO_2 yH_2O single crystals show a
broad electronic continuum with a pronounced peak around 100 cm-1 and a cutoff
at approximately 560 cm-1over a wide range of doping levels. The electronic
Raman spectra in superconducting and non-superconducting samples are similar at
room temperature, but evolve in markedly different ways with decreasing
temperature. For superconducting samples, the low-energy spectral weight is
depleted upon cooling below T* sim 150K, indicating a opening of a pseudogap
that is not present in non-superconducting materials. Weak additional phonon
modes observed below T* suggest that the pseudogap is associated with charge
ordering.Comment: 5 pages, 4 figures, for further information see www.peter-lemmens.d
Evaluating the Potential Efficacy of Invasive Lionfish (Pterois volitans) Removals
The lionfish, Pterois volitans (Linnaeus) and Pterois miles (Bennett), invasion of the Western Atlantic Ocean, Caribbean Sea and Gulf of Mexico has the potential to alter aquatic communities and represents a legitimate ecological concern. Several local removal programs have been initiated to control this invasion, but it is not known whether removal efforts can substantially reduce lionfish numbers to ameliorate these concerns. We used an age-structured population model to evaluate the potential efficacy of lionfish removal programs and identified critical data gaps for future studies. We used high and low estimates for uncertain parameters including: length at 50% vulnerability to harvest (Lvul), instantaneous natural mortality (M), and the Goodyear compensation ratio (CR). The model predicted an annual exploitation rate between 35 and 65% would be required to cause recruitment overfishing on lionfish populations for our baseline parameter estimates for M and CR (0.5 and 15). Lionfish quickly recovered from high removal rates, reaching 90% of unfished biomass six years after a 50-year simulated removal program. Quantifying lionfish natural mortality and the size-selective vulnerability to harvest are the most important knowledge gaps for future research. We suggest complete eradication of lionfish through fishing is unlikely, and substantial reduction of adult abundance will require a long-term commitment and may be feasible only in small, localized areas where annual exploitation can be intense over multiple consecutive years
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