A. Gozar

Crystal structure and high-field magnetism of La2CuO4

Neutron diffraction was used to determine the crystal structure and magnetic ordering pattern of a La2CuO4 single crystal, with and without applied magnetic field. A previously unreported, subtle monoclinic distortion of the crystal structure away from the orthorhombic space group Bmab was detected. The distortion is also present in lightly Sr-doped crystals. A refinement of the crystal structure shows that the deviation from orthorhombic symmetry is predominantly determined to drive a continuous reorientation of the copper spins from the orthorhombic b axis to the c axis, directly confirming predictions based on prior magnetoresistance and Raman scattering experiments. A spin-flop transition induced by a c-axis oriented field previously reported for nonstoichiometric La2CuO4 is also observed, but the transition field 11.5 T is significantly larger than that in the previous work.

Spin dynamics of Sr14Cu24O41 two-leg ladder studied by Raman spectroscopy.

The two-magnon (2M) excitation at 3000 cm(-1) in Sr14Cu24O41 two-leg ladder is studied by Raman scattering. A slight anisotropy of the superexchange coupling J(perpendicular)/J(parallel) approximately 0.8 with J(parallel) = 110+/-20 meV is proposed from the analysis of the magnetic scattering. The resonant coupling across the charge transfer gap increases the 2M intensity by orders of magnitude. The anisotropy of Raman scattering is dependent upon the excitation energy. The 2M relaxation is found to be correlated with the temperature dependent electronic Raman continuum at low frequencies.

Collective density-wave excitations in two-leg Sr14-xCaxCu24O41 ladders.

Raman measurements in the 1.5-20 cm(-1) energy range were performed on single crystals of Sr14-xCaxCu24O41. A quasielastic scattering peak (QEP) which softens with cooling is observed only in the polarization parallel to the ladder direction for samples with x=0, 8, and 12. The QEP is a Raman fingerprint of pinned collective density wave excitations screened by uncondensed carriers in the ladder structures. Our results suggest that transport in metallic samples, which is similar to transport in underdoped high-T(c) cuprates, is driven by a collective electronic response.

Magnetic order in lightly doped La2-xSrxCuO4.

We study long wavelength magnetic excitations in lightly doped La2-xSrxCuO4 (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 resonance, analyzed in terms of in-plane spin anisotropy, shows unconventional behavior within the AF state; it 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 Néel temperature in x=0.01.

Field dependence of the magnetic spectrum in anisotropic and Dzyaloshinskii-Moriya antiferromagnets. II. Raman spectroscopy

We compare the theoretical predictions of the previous paper on the field dependence of the magnetic spectrum in anisotropic two-dimensional and Dzyaloshinskii-Moriya layered antiferromagnets [L. Benfatto and M. B. Silva Neto, Phys. Rev. B 74, 024415 (2006)], with Raman spectroscopy experiments in

Collective Magnetic Excitations in SrCu2(BO3)2

{\mathrm{Sr}}_{2}\mathrm{Cu}{\mathrm{O}}_{2}{\mathrm{Cl}}_{2}

Spin dynamics and sliding density wave in Sr14Cu24O41 ladders

and untwinned

Antiferromagnetism in CaCu 3 Ti 4 O 12 studied by magnetic Raman spectroscopy

{\mathrm{La}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}

Sliding Density Wave in Sr14Cu24O41 Ladder Compounds

single crystals. We start by discussing the crystal structure and constructing the magnetic point group for the magnetically ordered phase of the two compounds,

Superconductivity-induced optical changes for energies of 100{Delta} in the cuprates

{\mathrm{Sr}}_{2}\mathrm{Cu}{\mathrm{O}}_{2}{\mathrm{Cl}}_{2}