High-performing superconducting YBa2Cu3O7–x (YBCO) films are fabricated by a chemical solution deposition methodology through novel barium-deficient low-fluorine solutions. The precursor solutions, distinguished for being straightforward, inexpensive and eco-friendly, allow us to reduce the growing temperature of YBCO down to 750 °C. We investigated the influence of the growing temperatures on both the microstructure and superconducting properties of YBCO films by using conventional thermal annealing and flash-heating approaches. A clear correlation between the growing temperature (Tg) and the superconducting performance of the films was obtained with improved performances observed at low Tg.

YBa2Cu3O7−x (YBCO) nanocomposites for wire applications need to operate in a broad range of frequencies, ranging from dc in magnets to GHz in cavities and screenings of future particle accelerators. We have investigated the in-field and angular vortex pinning performance in dc and at 50 GHz of two types of nanocomposites, pulsed laser deposition (PLD) YBCO with mixed Ba2YNbO6 + Ba2YTaO6 (BYNTO) nanorods and chemical solution deposited (CSD) YBCO with BaHfO3 (BHO) nanoparticles (NPs), and the pristine counterpart films, grown on top of single-crystalline substrates. Transport measurements performed up to 9 T between 5-77 K show that CSD nanocomposites exhibit a smooth field decay and increased single-tocollective crossover field H* compared to pristine samples, associated to the enhanced isotropic pinning contribution induced by the NPs, while PLD films exhibit unchanged H* and superior critical current densities up to higher irreversibility fields, associated to the anisotropic contribution introduced by the rods. Microwave in-field measurements of the pinning constant kp revealed CSD NCs exhibit a qualitatively similar, but smoother kp(H) than pristine samples, whereas for PLD samples, a growing kp(H) dependence is observed as a result of the increased relevance of the stiffness of the fluxons pinned by nanorods.

We report on the nonlinear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO, observed through high harmonic generation. While the linear optical response of the material is largely unchanged when cooling across the phase transitions, the nonlinear optical response sensitively imprints two critical points, one at the critical temperature of the cuprate with the exponential growth of the surface harmonic yield in the superconducting phase and another critical point, which marks the transition from strange metal to pseudogap phase. To reveal the underlying microscopic quantum dynamics, a strong-field quasi-Hubbard model was developed, which describes the measured optical response dependent on the formation of Cooper pairs. Further, the theory provides insight into the carrier scattering dynamics and allows us to differentiate between the superconducting, pseudogap, and strange metal phases. The direct connection between nonlinear optical response and microscopic dynamics provides a powerful methodology to study quantum phase transitions in correlated materials. Further implications are light wave control over intricate quantum phases, light–matter hybrids, and application for optical quantum computing.