Ultrafast Dynamics of Vibrational Symmetry Breaking in a Charge-ordered Nickelate

Abstract

The ability to probe symmetry breaking transitions on their natural time scales is one of the key challenges in nonequilibrium physics. Stripe ordering represents an intriguing type of broken symmetry, where complex interactions result in atomic-scale lines of charge and spin density. Although phonon anomalies and periodic distortions attest the importance of electron-phonon coupling in the formation of stripe phases, a direct time-domain view of vibrational symmetry breaking is lacking. We report experiments that track the transient multi-THz response of the model stripe compound La${}_{1.75}$Sr${}_{0.25}$NiO${}_4$, yielding novel insight into its electronic and structural dynamics following an ultrafast optical quench. We find that although electronic carriers are immediately delocalized, the crystal symmetry remains initially frozen - as witnessed by time-delayed suppression of zone-folded Ni-O bending modes acting as a fingerprint of lattice symmetry. Longitudinal and transverse vibrations react with different speeds, indicating a strong directionality and an important role of polar interactions. The hidden complexity of electronic and structural coupling during stripe melting and formation, captured here within a single terahertz spectrum, opens new paths to understanding symmetry breaking dynamics in solids.

21 pages, 4 figures; updated version with journal ref

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• Near-infrared light-induced superconducting-like state in underdoped YBa${}_2$Cu${}_3$O${}_y$ studied by $c$-axis terahertz third-harmonic generation
• Terahertz parametric amplification as a reporter of exciton condensate dynamics
• Ultrafast creation of a light induced semimetallic state in strongly excited 1T-TiSe${}_2$
• Time-resolved vibrational-pump visible-probe spectroscopy for thermal conductivity measurement of metal-halide perovskites
• Electronic transport through correlated electron systems with nonhomogeneous charge orderings
• Theory of time-resolved optical conductivity of superconductors:comparing two methods for its evaluation
• Violation of Luttinger's theorem in the simplest doped Mott insulator: Falicov-Kimball model in strong correlation limit
• Giant electron-phonon coupling of the breathing plane oxygen phonons in the dynamic stripe phase of La${}_{1.67}$Sr${}_{0.33}$NiO${}_4$
• Ultrafast optical melting of trimer superstructure in layered 1T'-TaTe2
• Ultrafast signatures of spin and orbital order in antiferromagnetic $\alpha$-Sr${}_2$CrO${}_4$