Stripe order and pseudogap state in YBa2Cu3O6+x as seen from magnon-assisted interband absorption

Charge and spin inhomogeneities are believed to be fundamental for understanding the normal and superconducting properties of YBa2Cu3O6+x and other cuprates. In the present paper, this problem is studied by optical interband absorption spectroscopy, which probes a quasi-static pattern of dynamical inhomogeneities. We investigated the temperature evolution of the exciton-bimagnon and exciton-two-magnon bands in metallic YBa2Cu3O6+x films in the pseudogap and superconducting states. Our results are indicative of a stripe structure which develops upon cooling in the pseudogap state and persists in the superconducting state. A correlation is found between the temperature behavior of the optical magnon-assisted features and the published data on temperature evolution of the neutron (π, π) resonance and muon spin depolarization rate. The continuum interband absorption is shown to be sensitive to the appearance of superconductivity in YBa2Cu3O6+x and NdBa2Cu3O6+x films. This effect is discussed in the framework of interrelation between the interband absorption and the kinetic energy.