Seminars Archive

X-ray and optical studies of light-controlled high-temperature superconductors

Abstract
The use of ultrashort optical and X-ray pulses offers new opportunities to study fundamental interactions in materials exhibiting unconventional quantum states, such as stripes, charge density waves and high-temperature superconductivity. To understand the microscopic interdependence between these order parameters, a probe capable of discerning their interaction on its natural length and time scales is necessary. In this colloquium, I will give an overview of ultrafast x-ray scattering and optical studies of complex materials revealing the coupled dynamics of order parameters. Particularly, I will focus on high temperature superconductors and recent ultrafast resonant soft x-ray scattering results tracking the transient evolution of charge density wave correlations in YBa2Cu3O6+x [S. Wandel et al., Science 376, 860 (2022)]. In this study, ultrashort infrared pulses produce a non-thermal quench of the superconducting state while X-ray pulses detect the reaction of charge density waves. The response happens on a picosecond timescale and is characterized by a large enhancement of spatial coherence of charge density waves, nearly doubling their correlation length, accompanied by a smaller increase of their amplitude. This ultrafast snapshot directly reveals the interaction between these quantum states on their natural timescales. It demonstrates that their competition manifests inhomogeneously at the nanoscale level, as disruption of spatial coherence, indicating the role of superconductivity in stabilizing topological defects within charge density waves domains. In conclusion, I will discuss ongoing developments at the LCLS to further expand on these results and unlock novel capabilities to control and observe quantum materials with light pulses.