261 research outputs found
Raman scattering through surfaces having biaxial symmetry
Magnetic Raman scattering in two-leg spin ladder materials and the
relationship between the anisotropic exchange integrals are analyzed by P. J.
Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
dependence of the two-magnon scattering is shown to provide information for the
magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
point out that the experimental results of polarized Raman measurements at
arbitrary angles with respect to the crystal axes have to be corrected for the
light ellipticity induced inside the optically anisotropic crystals. We refer
quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
for spectroscopic studies in other materials with strong anisotropy.Comment: To be published as a Comment in Phys. Rev.
Superconductivity in La(1.56)Sr(0.44)CuO(4)/La(2)CuO(4) superlattices
Superlattices of the repeated structure La(1.56)Sr(0.44)CuO(4)/La(2)CuO(4)
(LSCO-LCO), where none of the constituents is superconducting, show a
superconducting transition of T_c \simeq 25 K. In order to elucidate the nature
of the superconducting state we have performed a low-energy muSR study. By
applying a magnetic field parallel (Meissner state) and perpendicular (vortex
state) to the film planes, we could show that superconductivity is sheet like,
resulting in a very anisotropic superconducting state. This result is
consistent with a simple charge-transfer model, which takes into account the
layered structure and the difference in the chemical potential between LCO and
LSCO, as well as Sr interdiffusion. Using a pancake-vortex model we could
estimate a strict upper limit of the London penetration depth to 380 nm in
these superlattices. The temperature dependence of the muon depolarization rate
in field cooling experiments is very similar to what is observed in
intercalated BSCCO and suggests that vortex-vortex interaction is dominated by
electromagnetic coupling but negligible Josephson interaction.Comment: 4 pages, 3 figure
Charge collective modes in an incommensurately modulated cuprate
We report the first measurement of collective charge modes of insulating
Sr14Cu24O41 using inelastic resonant x-ray scattering over the complete
Brillouin zone. Our results show that the intense excitation modes at the
charge gap edge predominantly originate from the ladder-containing planar
substructures. The observed ladder modes (E vs. Q) are found to be dispersive
for momentum transfers along the "legs" but nearly localized along the "rungs".
Dispersion and peakwidth characteristics are similar to the charge spectrum of
1D Mott insulators, and we show that our results can be understood in the
strong coupling limit (U >> t_{ladder}> t_{chain}). The observed behavior is in
marked contrast to the charge spectrum seen in most two dimensional cuprates.
Quite generally, our results also show that momentum-tunability of inelastic
scattering can be used to resolve mode contributions in multi-component
incommensurate systems.Comment: 4+ pages, 5 figure
Magnon bands of N-leg integer-spin antiferromagnetic systems in the weak interchain-coupling regime
Using the exact results of the O(3) nonlinear sigma model (NLSM) and a few
quantitative numerical data for integer-spin antiferromagnetic (AF) chains, we
systematically estimate all magnon excitation energies of N-leg integer-spin AF
ladders and tubes in the weak-interchain-coupling regime. Our method is based
on a first-order perturbation theory for the strength of the interchain
coupling. It can deal with any kind of interchain interactions, in principle.
We confirm that results of the perturbation theory are in good agreement with
those of a quantum Monte Carlo simulation and with our recent study based on a
saddle-point approximation of the NLSM [Phys. Rev. B 72, 104438 (2005)]. Our
theory further supports the existence of a Haldane (gapped) phase even in a
d-dimensional (d\geq 2) spatially anisotropic integer-spin AF model, if the
exchange coupling in one direction is sufficiently strong compared with those
in all the other directions. The strategy in this paper is applicable to other
N-leg systems consisting of gapped chains which low-energy physics is exactly
or quantitatively known.Comment: 11 pages, 4 figures, Revtex, published version, see also
cond-mat/0506049 (PRB72, 104438 (2005)
Sliding Density-Wave in Sr_{14}Cu_{24}O_{41} Ladder Compounds
We used transport and Raman scattering measurements to identify the
insulating state of self-doped spin 1/2 two-leg ladders of Sr_{14}Cu_{24}O_{41}
as a weakly pinned, sliding density wave with non-linear conductivity and a
giant dielectric response that persists to remarkably high temperatures
Inhomogeneous CuO_{6} Tilt Distribution and Charge/Spin Correlations in La_{2-x-y}Nd_{y}Sr_{x}CuO$_{4} around commensurate hole concentration
Phononic and magnetic Raman scattering are studied in
LaNdSrCuO with three doping concentrations: x ~
1/8, y = 0; x ~ 1/8, y = 0.4; and x = 0.01, y = 0. We observe strong disorder
in the tilt pattern of the CuO_{6} octahedra in both the orthorhombic and
tetragonal phases which persist down to 10 K and are coupled to bond disorder
in the cation layers around 1/8 doping independent of Nd concentration. The
weak magnitude of existing charge/spin modulations in the Nd doped structure
does not allow us to detect the specific Raman signatures on lattice dynamics
or two-magnon scattering around 2200 cm-1.Comment: to be published in Phys. Rev.
Magnetic order in lightly doped La_{2-x}Sr_{x}CuO_{4}
We study long wavelength magnetic excitations in lightly doped
La_{2-x}Sr_{x}CuO_{4} (x < 0.03) detwinned crystals. The lowest energy magnetic
anisotropy induced gap can be understood in terms of the antisymmetric spin
interaction inside the antiferromagnetic (AF) phase. The second magnetic
resonace, analyzed in terms of in-plane spin anisotropy, shows unconventional
behavior within the AF state and led to the discovery of collective spin
excitations pertaining to a field induced magnetically ordered state. This
state persists in a 9 T field to more than 100 K above the N\'{e}el temperature
in x = 0.01.Comment: 5 pages, 5 figure
Derivation of the generalized Non Linear Sigma Model in the presence of the Dzyaloshinskii-Moriya interaction
We derive the long-wavelength non-linear sigma model for a two-dimensional
Heisenberg system in the presence of the Dzyaloshinskii-Moriya and
pseudodipolar interactions. We show that the system is a non-conventional
easy-axis antiferromagnet, displaying an anomalous coupling between the
magnetic field and the staggered order parameter. Our results are in good
agreement with recent experimental data for undoped La2CuO4 compounds.Comment: Proceedings of SCES05, to appear on Physica
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