Abstract

The application of transient terahertz (THz) pulses to excite and probe low-energy quantum and collective excitations in materials represents a powerful tool to study both intrinsic interactions and non-equilibrium phases. In the following, we discuss ultrafast multi-THz studies that resolve the dynamics of electronic itineracy and vibrational symmetries in a strongly-correlated nickelate. Many transition-metal oxides exhibit the emergence of “stripes,” corresponding to quasione- dimensional charge, spin and lattice modulations as a manifestation of strong correlations. In our experiments, optical excitation of a stripe-phase nickel oxide triggers the rapid melting of its atomic-scale charge order and results in dynamics that yields insight into the couplings underlying the stripes. The transient optical conductivity is sensitive to both charges and in-plane vibrations and reveals a succession of ultrafast processes, ranging from rapid delocalization and localization of charges, via a time-delayed reaction of vibrational distortions to the electronic quench, up to the multi-picosecond re-establishment of the symmetry-broken phase. 1