8 research outputs found
Thermal conductivity and specific heat of the linear chain cuprate SrCuO: Evidence for thermal transport via spinons
We report measurements of the specific heat and the thermal conductivity of
the model Heisenberg spin-1/2 chain cuprate SrCuO at low
temperatures. In addition to a nearly isotropic phonon heat transport, we find
a quasi one-dimensional excess thermal conductivity along the chain direction,
most likely associated with spin excitations (spinons). The spinon energy
current is limited mainly by scattering on defects and phonons. Analyzing the
specific heat data, the intrachain magnetic exchange is estimated to
be 2650 K.Comment: 4 RevTeX pages, 3 figures, to appear in Phys. Rev.
Electronic transport in EuB
EuB is a magnetic semiconductor in which defects introduce charge
carriers into the conduction band with the Fermi energy varying with
temperature and magnetic field. We present experimental and theoretical work on
the electronic magnetotransport in single-crystalline EuB. Magnetization,
magnetoresistance and Hall effect data were recorded at temperatures between 2
and 300 K and in magnetic fields up to 5.5 T. The negative magnetoresistance is
well reproduced by a model in which the spin disorder scattering is reduced by
the applied magnetic field. The Hall effect can be separated into an ordinary
and an anomalous part. At 20 K the latter accounts for half of the observed
Hall voltage, and its importance decreases rapidly with increasing temperature.
As for Gd and its compounds, where the rare-earth ion adopts the same Hund's
rule ground state as Eu in EuB, the standard antisymmetric
scattering mechanisms underestimate the of this contribution by several
orders of magnitude, while reproducing its almost perfectly. Well below
the bulk ferromagnetic ordering at = 12.5 K, a two-band model
successfully describes the magnetotransport. Our description is consistent with
published de Haas van Alphen, optical reflectivity, angular-resolved
photoemission, and soft X-ray emission as well as absorption data, but requires
a new interpretation for the gap feature deduced from the latter two
experiments.Comment: 35 pages, 12 figures, submitted to PR
Heat transport by lattice and spin excitations in the spin chain compounds SrCuO_2 and Sr_2CuO_3
We present the results of measurements of the thermal conductivity of the
quasi one-dimensional spin S=1/2 chain compound SrCuO_2 in the temperature
range between 0.4 and 300 K along the directions parallel and perpendicular to
the chains. An anomalously enhanced thermal conductivity is observed along the
chains. The analysis of the present data and a comparison with analogous recent
results for Sr_2CuO_3 and other similar materials demonstrates that this
behavior is generic for cuprates with copper-oxygen chains and strong
intrachain interactions. The observed anomalies are attributed to the
one-dimensional energy transport by spin excitations (spinons), limited by the
interaction between spin and lattice excitations. The energy transport along
the spin chains has a non-diffusive character, in agreement with theoretical
predictions for integrable models.Comment: 12 pages (RevTeX), 8 figure