Plane-polarized Raman continuum in the insulating and superconducting layered cuprates

Effect of transport current on suppression of superconductivity with ultrashort laser pulse

We study the suppression of superconductivity with ultrashort laser pulse in the presence of transport current. The theoretical model is based on the Bardeen-Cooper-Schrieffer relations for the superconducting state coupled with kinetic equations for nonequilibrium Bogoliubov quasiparticles and phonons. The results of numerical simulation for picosecond and femtosecond laser pulses of optical and infrared ranges are given. We discuss the effects of main problem parameters, including the current density.

Ultrafast magnetic dynamics in insulating YBa2Cu3O6.1 revealed by time resolved two-magnon Raman scattering

Measurement and control of magnetic order and correlations in real time is a rapidly developing scientific area relevant for magnetic memory and spintronics. In these experiments an ultrashort laser pulse (pump) is first absorbed by excitations carrying electric dipole moment. These then give their energy to the magnetic subsystem monitored by a time-resolved probe. A lot of progress has been made in investigations of ferromagnets but antiferromagnets are more challenging. Here, we introduce time-resolved two-magnon Raman scattering as a real time probe of magnetic correlations especially well-suited for antiferromagnets. Its application to the antiferromagnetic charge transfer insulator YBa₂Cu₃O_6.1 revealed rapid demagnetization within 90 fs of photoexcitation. The relaxation back to thermal equilibrium is characterized by much slower timescales. We interpret these results in terms of slow relaxation of the charge sector and rapid equilibration of the magnetic sector to a prethermal state characterized by parameters that change slowly as the charge sector relaxes.

Enhancing carrier generation in TiO2 by a synergistic effect between plasmon resonance in Ag nanoparticles and optical interference

Silver nanoparticles have been embedded at a few nanometer distance from the free surface of titania/silica multilayers using low energy ion beam synthesis. Transmission electron microscopy shows the presence of 3 nm-sized crystalline particles. Reflectance spectroscopy on these composite substrates shows an increase of the light capture efficiency in the visible range. This behaviour is interpreted as a synergistic effect between plasmon polariton resonance and Fabry-Perot interferences. Plasmon-resonant Raman spectroscopy is deeply used to analyze, on one hand confinement of vibrations and electronic excitations in Ag NPs, and on the other hand coupling of polar TiO2 phonons with injected photo-generated carriers. It is shown how these new Ag/TiO2 nanocomposite films appear as very promising to enhance the efficiency and enlarge the spectral sensitivity of plasmo-electronics devices.

On properly integrating the electronic Raman and optical infra-red spectra of high temperature superconducting cuprate materials

New electronic Raman and infra-red spectroscopy results from optimally and overdoped high temperature superconducting cuprate systems are interpreted in terms of the negative- U, boson-fermion crossover model. A distinction is made between those features which follow the condensate gap, 2Δ(p), and those that are set by the local pair binding energy, [Formula: see text]. The critical role of the doping level p(c) = 0.185 is highlighted in conjunction with the question of developing quasiparticle incoherence, making connection here with recent transport and related results. [Formula: see text] IR results for magnetic fields parallel and perpendicular to  c prove particularly illuminating. The general scheme developed continues to embrace all experimental data very satisfactorily.

Negative quantum interference between the electronic Raman scattering processes of CuO chains and CuO2 planes of heavily overdoped (Y, Ca)Ba2Cu3O(7-delta)

We found a strong X-Y anisotropy of the pair-breaking peak in the Raman scattering of heavily overdoped (Y, Ca)Ba2Cu3O(7-delta) (T(c) = 65 K). The pair-breaking peak is radically suppressed in the YY-polarized spectrum. We ascribe this anomaly to the effect of quantum interference between the Raman processes of the CuO-chain and the CuO2-plane electronic excitations that might take place as a result of the increase in the transfer matrix due to overdoping.