Direct Observation of k∥ and k⊥ Stripe Excitations in La2−xSrxCuO4

The superconducting transition temperature in the cuprate is pointed to be enhanced by the self-organized spin-charge separated stripes. The magnetic excitations are very different in k∥ and k⊥ stripes. Therefore if one detects the different excitations, it is a clear evidence of the stripe. Neutron scattering, however, always observes the mixed excitations. We first succeeded to detect the k⊥ stripe excitations of the separated dispersion induced by the super-lattice structure of the stripe in distinction from the k∥ stripe excitations by two-magnon Raman scattering. The stripe structure is ubiquitous in the whole carrier density range at low temperatures.