663 research outputs found
Comment on "Low Temperature Magnetic Instabilities in Triply Charged Fulleride Polymers" by D. Arcon et al., PRL 84, 562 (2000)
Recently, Arcon et al. reported ESR studies of the polymer phase (PP) of
Na_{2}Rb_{0.3}Cs_{0.7}C_{60} fulleride. It was claimed that this phase is a
quasi-one-dimensional metal above 45 K with a spin-gap below this temperature
and has antiferromagnetic(AF) order below 15 K, that is evidenced by
antiferromagnetic resonance(AFMR). For the understanding of the rich physics of
fullerides it is important to identify the different ground states. ESR has
proven to be a useful technique for this purpose. However, since it is a very
sensitive probe, it can detect a multitude of spin species and it is not
straightforward to identify their origin, especially in a system like
Na_{2}Rb_{x}Cs_{1-x}C_{60} with three dopants, when one part of the sample
polymerizes but the majority does not. The observation of a low dimensional
instability in the single bonded PP would be a novel and important result.
Nevertheless, in this Comment we argue that Na_{2}Rb_{0.3}Cs_{0.7}C_{60} is not
a good choice for this purpose since, as we show, the samples used by Arcon et
al. are inhomogeneous. We point out that recent results on the PP of
Na_{2}CsC_{60} contradicts the observation of low dimensional instabilities in
Na_{2}Rb_{0.3}Cs_{0.7}C_{60}.Comment: 1 pags, no figure
Optical evidence for a magnetically driven structural transition in the spin web
is a modest frustrated spin system, which undergoes an
anti-ferromagnetic transition at . The anti-ferromagnetic spin
alignment in below is supposed to induce a magneto-elastic
strain of the lattice. The complete absorption spectrum of is
obtained through Kramers-Kronig transformation of the optical reflectivity,
measured from the far-infrared up to the ultraviolet spectral range as a
function of temperature (). Below , we find a new mode at
208 . The spectral weight associated to this additional mode increases
as with decreasing below . The implication of
the optical findings will be discussed in relation to the magnetic phase
transition at .Comment: 9 pages, 3 figure
Bi2Te_xSe_y series studied by resistivity and thermopower
We study the detailed temperature and composition dependence of the
resistivity, , and thermopower, , for a series of layered
bismuth chalcogenides BiTeSe, and report the stoichiometry
dependence of the optical band gap. In the resistivity of the most compensated
member, BiTeSe, we find a low-temperature plateau whose
onset temperature correlates with the high-temperature activation energy. For
the whole series can be described by a simple model for an extrinsic
semiconductor. By substituting Se for Te, the Fermi level is tuned from the
valence band into the conduction band. The maximum values of , bulk band
gap as well the activation energy in the resistivity are found for
An update on the inland cladoceran and copepod fauna of Belgium, with a note on the importance of temporary waters
Interference and Interaction in Multiwall Carbon Nanotubes
We report equilibrium electric resistance R and tunneling spectroscopy dI/dV
measurements obtained on single multiwall nanotubes contacted by four metallic
Au fingers from above. At low temperature quantum interference phenomena
dominate the magnetoresistance. The phase-coherence and elastic-scattering
lengths are deduced. Because the latter is of order of the circumference of the
nanotubes, transport is quasi-ballistic. This result is supported by a dI/dV
spectrum which is in good agreement with the density-of-states (DOS) due to the
one-dimensional subbands expected for a perfect single-wall tube. As a function
of temperature T the resistance increases on decreasing T and saturates at
approx. 1-10 K for all measured nanotubes. R(T) cannot be related to the
energy-dependent DOS of graphene but is mainly caused by interaction and
interference effects. On a relatively small voltage scale of order 10 meV, a
pseudogap is observed in dI/dV which agrees with Luttinger-Liquid theories for
nanotubes. Because we have used quantum diffusion based on Fermi-Liquid as well
as Luttinger-Liquid theory in trying to understand our results, a large
fraction of this paper is devoted to a careful discussion of all our results.Comment: 14 pages (twocolumn), 8 figure
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