9 research outputs found
Anisotropic spin freezing in the S=1/2 zigzag ladder compound SrCuO2
Using magnetic neutron scattering we characterize an unusual low temperature
phase in orthorhombic SrCuO2. The material contains zigzag spin ladders formed
by pairs of S=1/2 chains (J=180 meV) coupled through a weak frustrated
interaction |J'|<0.1J. At T<Tc1=5.0(4)K an elastic peak develops in a gapless
magnetic excitation spectrum indicating spin freezing on a time scale larger
than 200 picoseconds. While the frozen state has long range commensurate
antiferromagnetic order along the chains with the correlation length exceeding
200 lattice periods along the c-axis and a substantial correlation length of
60(25) spacings along the a-axis perpendicular to the zigzag plane, only 2
lattice units are correlated along the b-axis which is the direction of the
frustrated interactions. The frozen magnetic moment of each Cu ion is very
small, 0.033(7) Bohr magneton even at T=0.35K, and has unusual temperature
dependence with a cusp at Tc2=1.5K reminiscent of a phase transition. We argue
that slow dynamics of stripe-like cooperative magnetic defects in tetragonal
a-c planes yield this anisotropic frozen state.Comment: 4 pages, LaTeX, submitted to PR
The unusual electronic structure of the "pseudo-ladder" compound CaCu2O3
Experimental and theoretical studies of the unoccupied electronic structure
of CaCu2O3 single crystals have been performed using polarization-dependent
x-ray absorption spectroscopy and band structure calculations. The measured
hole distribution shows an unusual large number of holes in orbitals parallel
to the interlayer direction which is in agreement with the theoretical
analysis. CaCu2O3 deviates significantly from the standard pd-sigma cuprate
picture. The corresponding strong interlayer exchange is responsible for the
missing spin gap generic for other two-leg ladder cuprates.Comment: 4 pages, 3 figures include
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.