Self-organized electronically ordered phases are a recurring feature in correlated materials, resulting in, for example, fluctuating charge stripes whose role in high-T C superconductivity is under debate. However, the relevant cause-effect relations between real-space charge correlations and low-energy excitations remain hidden in time-averaged studies. Here we reveal ultrafast charge localization and lattice vibrational coupling as dynamic precursors of stripe formation in the model compound La 1.75 Sr 0.25 NiO 4, using ultrafast and equilibrium mid-infrared spectroscopy. The opening of a pseudogap at a crossover temperature T * far above long-range stripe formation establishes the onset of electronic localization, which is accompanied by an enhanced Fano asymmetry of Ni-O stretch vibrations. Ultrafast excitation triggers a sub-picosecond dynamics exposing the synchronous modulation of electron-phonon coupling and charge localization. These results illuminate the role of localization in forming the pseudogap in nickelates, opening a path to understanding this mysterious phase in a broad class of complex oxides.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)