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Flannigan_CAP CDW Coupling_Combined.pdf (1.83 MB)

Coherent Phonon Disruption and Lock-In During a Photoinduced Charge-Density-Wave Phase Transition

submitted on 01.04.2021, 23:03 and posted on 05.04.2021, 04:34 by Spencer A. Reisbick, Yichao Zhang, Jialiang Chen, Paige Engen, David Flannigan
Ultrafast manipulation of phases and phase domains in quantum materials is a key approach to unraveling and harnessing interwoven effects of charge and lattice degrees of freedom. In the intensely-studied charge-density-wave (CDW) material, 1T-TaS2, phonon coupling to periodic lattice distortions (PLDs) and atomically-incoherent picosecond structural phase transitions suggest transitional periods could exist for delayed onset of mode coherence. Here we find evidence for such a connection between displacively-excited coherent acoustic phonons and PLDs using 4D ultrafast electron microscopy. Following femtosecond optical excitation of an ultrathin crystal, a propagating hybridized mode is imaged emerging from linear defects within a 1-μm region. Partial coherence and low amplitudes during onset of the incommensurate phase convert to higher-amplitude, increasingly-coherent oscillations as phase-growth stabilizes. The hybrid mode consists of large out-of-plane distortions coupled to basal-plane bond oscillations propagating at anomalously high velocities. The strongly-correlated behaviors observed here represent a potential means to control phase behaviors in quantum materials using defect-engineered coherent-phonon seeding.




American Chemical Society Petroleum Research Fund


Louise T. Dosdall Fellowship


Email Address of Submitting Author


University of Minnesota



ORCID For Submitting Author


Declaration of Conflict of Interest

The authors declare no competing financial interest.