title: Ultrafast charge localization in a stripe-phase nickelate.
abstract: Self-organized electronically ordered phases are a recurring feature in correlated materials, resulting in, for example, fluctuating charge stripes whose role in high-TC 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)NiO4, 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.
authors.affiliation: Materials Sciences Division, E. O. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
authors.forename: G
authors.initials: G
authors.lastname: Coslovich
authors.forename: B
authors.initials: B
authors.lastname: Huber
authors.forename: W-S
authors.initials: WS
authors.lastname: Lee
authors.forename: Y-D
authors.initials: YD
authors.lastname: Chuang
authors.forename: Y
authors.initials: Y
authors.lastname: Zhu
authors.forename: T
authors.initials: T
authors.lastname: Sasagawa
authors.forename: Z
authors.initials: Z
authors.lastname: Hussain
authors.forename: H A
authors.initials: HA
authors.lastname: Bechtel
authors.forename: M C
authors.initials: MC
authors.lastname: Martin
authors.forename: Z-X
authors.initials: ZX
authors.lastname: Shen
authors.forename: R W
authors.initials: RW
authors.lastname: Schoenlein
authors.forename: R A
authors.initials: RA
authors.lastname: Kaindl