303 research outputs found
Hour-glass magnetic spectrum in a stripe-less insulating transition metal oxide
An hour-glass shaped magnetic excitation spectrum appears to be an universal
characteristic of the high-temperature superconducting cuprates. Fluctuating
charge stripes or alternative band structure approaches are able to explain the
origin of these spectra. Recently, an hour- glass spectrum has been observed in
an insulating cobaltate, thus, favouring the charge stripe scenario. Here we
show that neither charge stripes nor band structure effects are responsible for
the hour-glass dispersion in a cobaltate within the checkerboard charge ordered
regime of La2-xSrxCoO4. The search for charge stripe ordering reflections
yields no evidence for charge stripes in La1.6Sr0.4CoO4 which is supported by
our phonon studies. With the observation of an hour-glass-shaped excitation
spectrum in this stripe-less insulating cobaltate, we provide experimental
evidence that the hour-glass spectrum is neither necessarily connected to
charge stripes nor to band structure effects, but instead, probably intimately
coupled to frustration and arising chiral or non-collinear magnetic
correlations
Model independent tests of the Kerr bound with extreme mass ratio inspirals
An outstanding prediction of general relativity is the fact that the angular momentum S of an isolated black hole with mass μ is limited by the Kerr bound, S≤Gμ2/c. Testing this cornerstone is challenging due to the difficulty in modeling spinning compact objects that violate this bound. We argue that precise, model-independent tests can be achieved by measuring gravitational waves from an extreme mass ratio inspiral around a supermassive object, one of the main targets of the future LISA mission. In the extreme mass ratio limit, the dynamics of the small compact object depends only on its multipole moments, which are free parameters. At variance with the comparable-mass case, accurate waveforms are valid also when the spin of the small object greatly exceeds the Kerr bound. By computing the orbital dephasing and the gravitational-wave signal emitted by a spinning point particle in circular, nonprecessing, equatorial motion around a Kerr black hole, we estimate that LISA will be able to measure the spin of the small compact object at the level of 10%. Together with mass measurements, this will allow for theory-agnostic, unprecedented constraints on string-theory inspired objects such as “superspinars”, almost in their entire parameter space
Editorial: Polymer materials for energy storage and harvesting, and other sustainable applications
One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6
Using inelastic neutron scattering, we have observed a quasi-one-dimensional
dispersive magnetic excitation in the frustrated triangular-lattice spin-2
chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
characterized by a large zone-center spin gap of ~27 meV, which we attribute to
the large single-ion anisotropy, and disperses along the chain direction with a
bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
measurable dispersion was found. With increasing temperature, the magnon
dispersion shifts towards lower energies, yet persists up to at least 150 K,
indicating that the ferromagnetic intrachain correlations survive up to 6 times
higher temperatures than the long-range interchain antiferromagnetic order. The
magnon dispersion can be well described within the predictions of linear
spin-wave theory for a system of weakly coupled ferromagnetic chains with large
single-ion anisotropy, enabling the direct quantitative determination of the
magnetic exchange and anisotropy parameters.Comment: 7 pages, 6 figures including one animatio
Spin pseudogap in Ni-doped SrCuO2
The S=1/2 spin chain material SrCuO2 doped with 1% S=1 Ni-impurities is
studied by inelastic neutron scattering. At low temperatures, the spectrum
shows a pseudogap \Delta ~ 8 meV, absent in the parent compound, and not
related to any structural phase transition. The pseudogap is shown to be a
generic feature of quantum spin chains with dilute defects. A simple model
based on this idea quantitatively accounts for the exprimental data measured in
the temperature range 2-300 K, and allows to represent the momentum-integrated
dynamic structure factor in a universal scaling form.Comment: 5 pages, 3 figure
Inelastic neutron scattering study of the H2 interaction with carbon-supported Pt and Pd catalysts
Diagnostic and therapeutic management of Cryptococcosis in a kitten with practical considerations to veterinary pediatric therapeutic approach
The Effect of Al-Alkyls on the Phillips Catalyst for Ethylene Polymerization: The Case of Diethylaluminum Ethoxide (DEALE)
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