Nanoscale Charge-order Dynamics in Stripe-phase Nickelates Probed via Ultrafast THz Spectroscopy

摘要

We discuss equilibrium and ultrafast optical pump-THz probe spectroscopy of the model stripe-ordered system La_(1.75)Sr_(0.25)NiO_4. We present a multi-oscillator analysis of the phonon bending mode splitting observed at low temperatures in equilibrium, along with a variational model for the transient THz reflectivity variations. The low temperature splitting is directly related to the formation of the long-range stripe-order, while the background conductivity is reminiscent of the opening of the mid-IR pseudogap. Ultrafast experiments in the multi-THz spectral range show strong THz reflectivity variations around the phonon bending mode frequency (≈11 THz).