Ultrafast charge localization in a stripe-phase nickelate

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spectroscopy

Background:

• Self-organized electronic phases, like charge stripes, are common in correlated materials.
• The relationship between charge correlations and low-energy excitations is not fully understood due to limitations of time-averaged studies.
• The role of charge stripes in high-temperature superconductivity remains a subject of debate.

Purpose of the Study:

• To investigate the dynamic precursors of stripe formation in the model compound La(1.75)Sr(0.25)NiO4.
• To elucidate the interplay between ultrafast charge localization and lattice vibrational coupling.
• To understand the role of electronic localization in the formation of the pseudogap phase in nickelates.

Main Methods:

• Utilized ultrafast and equilibrium mid-infrared spectroscopy.
• Analyzed the dynamics of charge localization and electron-phonon coupling.
• Investigated the Fano asymmetry of Ni-O stretch vibrations.

Main Results:

• Observed electronic localization initiating at a crossover temperature (T*) above long-range stripe formation.
• Detected enhanced Fano asymmetry in Ni-O vibrations, indicating coupled electron-phonon interactions.
• Revealed sub-picosecond dynamics upon ultrafast excitation, showing synchronous modulation of electron-phonon coupling and charge localization.

Conclusions:

• Ultrafast charge localization and lattice vibrational coupling act as dynamic precursors to stripe formation.
• Electronic localization plays a crucial role in forming the pseudogap in nickelates.
• These findings provide insights into a mysterious phase in complex oxides and its connection to superconductivity.