65 research outputs found
Magnon Heat Transport in (Sr,La)_14Cu_24O_41
We have measured the thermal heat conductivity kappa of the compounds
Sr_14Cu_24O_41 and Ca_9La_5Cu_24O_41 containing doped and undoped spin ladders,
respectively. We find a huge anisotropy of both, the size and the temperature
dependence of kappa which we interpret in terms of a very large heat
conductivity due to the magnetic excitations of the one-dimensional spin
ladders. This magnon heat conductivity decreases with increasing hole doping of
the ladders. The magnon heat transport is analyzed theoretically using a simple
kinetic model. From this analysis we determine the spin gap and the temperature
dependent mean free path of the magnons which ranges by several thousand
angstroms at low temperature. The relevance of several scattering channels for
the magnon transport is discussed.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Magnon-Hole Scattering and Charge Order in
The magnon thermal conductivity of the hole doped
spin ladders in has been investigated at low
doping levels . The analysis of reveals a strong
doping and temperature dependence of the magnon mean free path
which is a local probe for the interaction of magnons with
the doped holes in the ladders. In particular, this novel approach to studying
charge degrees of freedom via spin excitations shows that charge ordering of
the holes in the ladders leads to a freezing out of magnon-hole scattering
processes
Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination
The magnon thermal conductivity of the spin ladders
in has been investigated at low doping levels
, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic
defects which define an upper limit for and therefore allow
a clear-cut relation between and to
be established independently of any model. Over a large temperature range we
observe a progressive suppression of with increasing
Zn-content and find in particular that with respect to pure is strongly suppressed even in
the case of tiny impurity densities where ~{\AA}.
This shows unambiguously that large ~{\AA} which
have been reported for and on basis of a kinetic model are in the correct order
of magnitude
Plasmons and Interband Transitions of CaSrCuO investigated by Electron Energy-Loss Spectroscopy
Electron energy-loss spectroscopy studies have been performed in order to get
a deeper insight into the electronic structure and elementary excitations of
the two-leg ladder system CaSrCuO. We find a strong
anisotropy of the loss function for momentum transfers along the a and
c-crystallographic axis, and a remarkable linear plasmon dispersion for a
momentum transfer parallel to the legs of the ladders. The investigated
spectral features are attributed to localized and delocalized charge-transfer
excitations and the charge carrier plasmon. The charge carrier plasmon position
and dispersion in the long wave-length limit agree well with expectations based
upon the band structure of the two-leg ladder, while the observed quasi-linear
plasmon dispersion might be related to the peculiar properties of underdoped
cuprates in general.Comment: 16 pages, 8 figure
Optical spectroscopy of (La,Ca)14Cu24O41 spin ladders: comparison of experiment and theory
Transmission and reflectivity of La_x Ca_14-x Cu_24 O_41 two-leg spin-1/2
ladders were measured in the mid-infrared regime between 500 and 12000 1/cm.
This allows us to determine the optical conductivity sigma_1 directly and with
high sensitivity. Here we show data for x=4 and 5 with the electrical field
polarized parallel to the rungs (E||a) and to the legs (E||c). Three
characteristic peaks are identified as magnetic excitations by comparison with
two different theoretical calculations.Comment: 4 pages, 2 figures, submitted to SCES 200
Comment on "Frustrating interactions and broadened magnetic interactions in the edge-sharing CuO_2 chains in La_5 Ca_9 Cu_24 O_41"
Using Monte Carlo techniques, we show that the two--dimensional anisotropic
Heisenberg model reproducing nicely inelastic neutron scattering measurements
on La_5 Ca_9 Cu_24 O_41 (Matsuda et al. [Phys. Rev. B 68, 060406(R) (2003)])
seems to be insufficient to describe correctly measurements on thermodynamic
quantities like the magnetization or the susceptibility. Possible reasons for
the discrepancy are suggested.Comment: 3 pages, 2 EPS figures; part (ii) rewritten, some typos corrected;
final version that has been accepted for publication in Phys. Rev.
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