The individual kparallel and kperp stripe excitations in fluctuating spin-charge stripes have not been observed yet. In Raman scattering if we set, for example, incident and scattered light polarizations to two possible stripe directions, we can obse
rve the fluctuating stripe as if it is static. Using the different symmetry selection rule between the B1g two-magnon scattering and the B1g and B2g isotropic electronic scattering, we succeeded to obtain the kparallel and kperp strip magnetic excitations separately in La2-xSrxCuO4. Only the kperp stripe excitations appear in the wide-energy isotropic electronic Raman scattering, indicating that the charge transfer is restricted to the direction perpendicular to the stripe. This is the same as the Burgers vector of an edge dislocation which easily slides perpendicularly to the stripe. Hence charges at the edge dislocation move together with the dislocation perpendicularly to the stripe, while other charges are localized. A looped edge dislocation has lower energy than a single edge dislocation. The superconducting coherence length is close to the inter-charge stripe distance at x le 0.2. Therefore we conclude that Cooper pairs are formed at looped edge dislocations. The restricted charge transfer direction naturally explains the opening of a pseudogap around (0, {pi}) for the stripe parallel to the b axis and the reconstruction of the Fermi surface to have a flat plane near (0, {pi}). They break the four-fold rotational symmetry. Furthermore the systematic experiments revealed the carrier density dependence of the isotropic and anisotropic electronic excitations, the spin density wave and/or charge density wave gap near ({pi}/2, {pi}/2), and the strong coupling between the electronic states near ({pi}/2, {pi}/2) and the zone boundary phonons at ({pi}, {pi}).
Raman selection rules for electronic and magnetic excitations in BaFe2As2 were theoretically investigated and applied them to the separate detection of the nodal and anti-nodal gap excitations at the spin density wave (SDW) transition and the separat
e detection of the nearest and the next nearest neighbor exchange interaction energies. The SDW gap has Dirac nodes, because many orbitals participate in the electronic states near the Fermi energy. Using a two-orbital band model the electronic excitations near the Dirac node and the anti-node are found to have different symmetries. Applying the symmetry difference to Raman scattering the nodal and anti-nodal electronic excitations are separately obtained. The low-energy spectra from the anti-nodal region have critical fluctuation just above TSDW and change into the gap structure by the first order transition at TSDW, while those from the nodal region gradually change into the SDW state. The selection rule for two-magnon scattering from the stripe spin structure was obtained. Applying it to the two-magnon Raman spectra it is found that the magnetic exchange interaction energies are not presented by the short-range superexchange model, but the second derivative of the total energy of the stripe spin structure with respect to the moment directions. The selection rule and the peak energy are expressed by the two-magnon scattering process in an insulator, but the large spectral weight above twice the maximum spin wave energy is difficult to explain by the decayed spin wave. It may be explained by the electronic scattering of itinerant carriers with the magnetic self-energy in the localized spin picture or the particle-hole excitation model in the itinerant spin picture. The magnetic scattering spectra are compared to the insulating and metallic cuprate superconductors whose spins are believed to be localized.
Two magnon excitations and the nodal spin density wave (SDW) gap were observed in BaFe2As2 by Raman scattering. Below the SDW transition temperature (TSDW) nodal SDW gap opens together with new excitations in reconstructed electronic states. The two-
magnon peak remains above TSDW and moreover the energy increases a little. The change from the long-range ordered state to the short-range correlated state is compared to the cuprate superconductors.
