L. Capogna

Dispersion of the odd magnetic resonant mode in near-optimally doped Bi2Sr2CaCu2O8+δ

We report a neutron scattering study of the spin excitation spectrum in the superconducting state of the slightly overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} system (T{sub c}=87 K). We focus on the dispersion of the resonance peak in the superconducting state that is due to a S=1 collective mode. The measured spin excitation spectrum bears a strong similarity to the spectrum of the YBa{sub 2}Cu{sub 3}O{sub 6+x} system for a similar doping level (i.e., x{approx}0.95-1), which can be described as intersecting upward- and downward-dispersing branches. A close comparison of the threshold of the electron-hole spin flip continuum, known from angle resolved photoemission measurements in the same system, indicates that the magnetic response in the superconducting state is confined, in both energy and momentum, below the gapped Stoner continuum. In contrast to YBa{sub 2}Cu{sub 3}O{sub 6+x}, the spin excitation spectrum is broader than the experimental resolution. In the framework of an itinerant-electron model, we quantitatively relate this intrinsic energy width to the superconducting gap distribution observed in scanning tunneling microscopy experiments. Our study further suggests a significant in-plane anisotropy of the magnetic response.

Odd and even magnetic resonant modes in highly overdoped Bi2Sr2CaCu2O8+δ

We present inelastic neutron scattering data on highly overdoped Bi_2 Sr_2 Ca Cu_2 O_{8+\delta} single crystals with superconducting transition temperature T_C=70 K and, for comparison, a nearly optimally doped crystal with T_C=87 K. In both samples, magnetic resonant modes with odd and even symmetry under exchange of the two CuO_2 layers in the unit cell are observed. In the overdoped sample, the linewidth of the odd mode is reduced compared with the optimally doped sample. This finding is discussed in conjunction with recent evidence for intrinsic inhomogeneities in this compound. The data on odd and even resonant excitations are otherwise fully consistent with trends established on the basis of data on YBa_2Cu_3O_{6+x}. This confirms the universality of these findings and extends them into the highly overdoped regime of the phase diagram.

Magnetic structure of the edge-sharing copper oxide chain compound NaCu 2 O 2

Single-crystal neutron diffraction has been used to determine the incommensurate magnetic structure of

Magnetic excitations and phonons in the spin-chain compound Na Cu 2 O 2

{\text{NaCu}}_{2}{\text{O}}_{2}

Helicoidal magnetic order in a clean copper oxide spin chain compound

, a compound built up of chains of edge-sharing

Inelastic neutron scattering study of spin excitations in the superconducting state of high temperature superconductors

{\text{CuO}}_{4}

Flux-growth and characterization of NaCu2O2 single crystals

plaquettes. Magnetic structures compatible with the lattice symmetry were identified by a group-theoretical analysis and their magnetic structure factors were compared to the experimentally observed Bragg intensities. In conjunction with other experimental data, this analysis yields an elliptical helix structure in which both the helicity and the polarization plane alternate among copper-oxide chains. This magnetic ground state is discussed in the context of the recently reported multiferroic properties of other copper-oxide chain compounds.

Phase equilibria and NaCu2O2 crystal growth in the Na–Cu–O system

We report an inelastic light scattering study of single-crystalline

Flux-growth and characterization of NaCu 2O 2 single crystals

\mathrm{Na}{\mathrm{Cu}}_{2}{\mathrm{O}}_{2}

Neutron scattering/Diffusion de neutrons Inelastic neutron scattering study of spin excitations in the superconducting state of high temperature superconductors

, a spin-chain compound known to exhibit a phase with helical magnetic order at low temperatures. Phonon excitations were studied as a function of temperature and light polarization, and the phonon frequencies are compared to the results of ab initio lattice dynamical calculations, which are also reported here. The good agreement between the observed and calculated modes allows an assignment of the phonon eigenvectors. Two distinct high-energy two-magnon features as well as a sharp low-energy one-magnon peak were also observed. These features are discussed in terms of the magnon modes expected in a helically ordered state. At high temperatures, the spectral features attributable to magnetic excitations are replaced by a broad, quasielastic mode due to overdamped spin excitations.