720 research outputs found
Photoemission kinks and phonons in cuprates
One of the possible mechanisms of high Tc superconductivity is Cooper pairing
with the help of bosons, which change the slope of the electronic dispersion as
observed by photoemission. Giustino et al. calculated that in the high
temperature superconductor La1.85Sr0.15CuO4 crystal lattice vibrations
(phonons) should have a negligible effect on photoemission spectra and
concluded that phonons do not play an important role. We show that the
calculations employed by Giustino et al. fail to reproduce huge influence of
electron-phonon coupling on important phonons observed in experiments. Thus one
would expect these calculations to similarly fail in explaining the role of
electron-phonon coupling for the electronic dispersion.Comment: To appear in Nature as a Brief Communiction Arisin
Oxygen phonon branches in overdoped LaSrCuO
The dispersion of the Cu-O bond-stretching vibrations in overdoped
LaSrCuO (not superconducting) has been studied by high
resolution inelastic neutron scattering. It was found that the doping-induced
renormalization of the so-called breathing and the half-breathing modes is
larger than in optimally doped LaSrCuO. On the other
hand, the phonon linewidths are generally smaller in the overdoped sample.
Features observed in optimally doped LaSrCuO which
suggest a tendency towards charge stripe formation are absent in overdoped
LaSrCuO.Comment: 6 pages, 8 figure
Dynamics of Vortex Pair in Radial Flow
The problem of vortex pair motion in two-dimensional plane radial flow is
solved. Under certain conditions for flow parameters, the vortex pair can
reverse its motion within a bounded region. The vortex-pair translational
velocity decreases or increases after passing through the source/sink region,
depending on whether the flow is diverging or converging, respectively. The
rotational motion of two corotating vortexes in a quiescent environment
transforms into motion along a logarithmic spiral in the presence of radial
flow. The problem may have applications in astrophysics and geophysics.Comment: 13 pages, 9 figure
Continuous input nonlocal games
We present a family of nonlocal games in which the inputs the players receive
are continuous. We study three representative members of the family. For the
first two a team sharing quantum correlations (entanglement) has an advantage
over any team restricted to classical correlations. We conjecture that this is
true for the third member of the family as well.Comment: Journal version, slight modification
Raman scattering in a two-dimensional electron gas: Boltzmann equation approach
The inelastic light scattering in a 2-d electron gas is studied theoretically
using the Boltzmann equation techniques. Electron-hole excitations produce the
Raman spectrum essentially different from the one predicted for the 3-d case.
In the clean limit it has the form of a strong non-symmetric resonance due to
the square root singularity at the electron-hole frequency while
in the opposite dirty limit the usual Lorentzian shape of the cross section is
reestablished. The effects of electromagnetic field are considered
self-consistently and the contribution from collective plasmon modes is found.
It is shown that unlike 3-d metals where plasmon excitations are unobservable
(because of very large required transfered frequencies), the two-dimensional
electron system gives rise to a low-frequency ()
plasmon peak. A measurement of the width of this peak can provide data on the
magnitude of the electron scattering rate.Comment: 4 pages, 3 figures. to appear in Phys. Rev. B 59 (1999
Electron-phonon anomaly related to charge stripes: static stripe phase versus optimally-doped superconducting La1.85Sr0.15CuO4
Inelastic neutron scattering was used to study the Cu-O bond-stretching
vibrations in optimally doped La1.85Sr0.15CuO4 (Tc = 35 K) and in two other
cuprates showing static stripe order at low temperatures, i.e.
La1.48Nd0.4Sr0.12CuO4 and La1.875Ba0.125CuO4. All three compounds exhibit a
very similar phonon anomaly, which is not predicted by conventional band
theory. It is argued that the phonon anomaly reflects a coupling to charge
inhomogeneities in the form of stripes, which remain dynamic in superconducting
La1.85Sr0.15CuO4 down to the lowest temperatures. These results show that the
phonon effect indicating stripe formation is not restricted to a narrow region
of the phase diagram around the so-called 1/8 anomaly but occurs in optimally
doped samples as well.Comment: to appear in J. Low Temp. Phy
Competition between commensurate and incommensurate magnetic ordering in Fe(1+y)Te
The Fe1+y Te1-x Sex compounds belong to the family of iron-based high
temperature superconductors, in which superconductivity often appears upon
doping antiferromagnetic parent compounds. Unlike other Fe-based
superconductors (in which the antiferromagnetic order is at the Fermi surface
nesting wavevector [1/2,1/2,1]), the Fe1+y Te1-x Sex parent compound Fe1+y Te
orders at a different wavevector, [1/2, 0, 1/2]. Furthermore, the ordering
wavevector depends on y, the occupation of interstitial sites with excess iron;
the origin of this behavior is controversial. Using inelastic neutron
scattering on Fe1.08 Te, we find incommensurate magnetic fluctuations above the
Neel temperature, even though the ordered state is bicollinear and commensurate
with gapped spin waves. This behavior can be understood in terms of a
competition between commensurate and incommensurate order, which we explain as
a lock-in transition caused by the magnetic anisotropy
Magnetic Blue Phase in the Chiral Itinerant Magnet MnSi
Chiral nematic liquid crystals sometimes form blue phases characterized by
spirals twisting in different directions. By combining model calculations with
neutron-scattering experiments, we show that the magnetic analogue of blue
phases does form in the chiral itinerant magnet MnSi in a large part of the
phase diagram. The properties of this blue phase explain a number of previously
reported puzzling features of MnSi such as partial magnetic order and a
two-component specific-heat and thermal-expansion anomaly at the magnetic
transition
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