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Phase ordering of charge density waves traced by ultrafast low-energy electron diffraction


We introduce ultrafast low-energy electron diffraction (ULEED) in backscattering for the study of structural dynamics at surfaces. Using a tip-based source of ultrashort electron pulses, we investigate the optically driven transition between charge density wave phases at the surface of 1T-TaS2. The large transfer width of the instrument allows us to employ spot-profile analysis, resolving the phase-ordering kinetics in the nascent incommensurate charge density wave phase. We observe a coarsening that follows a power-law scaling of the correlation length, driven by the annihilation of dislocation-type topological defects of the charge-ordered lattice. Our work opens up the study of a wide class of structural transitions and ordering phenomena at surfaces and in low-dimensional systems.

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Figure 1: ULEED set-up and high-resolution diffraction pattern from 1T-TaS2.
Figure 2: ULEED of the structural phase transition between CDW phases.
Figure 3: Phase-ordering kinetics of IC CDW governed by topological defects.
Figure 4: Numerical simulation of phase-ordering kinetics.


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This work was funded by the European Research Council (ERC Starting Grant ‘ULEED’, ID: 639119) and the Deutsche Forschungsgemeinschaft (SFB-1073, project A05). We gratefully acknowledge insightful discussions with S. V. Yalunin and A. Zippelius. Furthermore we thank K. Hanff for help with sample preparation.

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The project was planned by S.V., G.S., S.Schramm, S.Schäfer and C.R. Experiments and data analysis were conducted by S.V. and G.S., with contributions from J.G.H., T.D. and M.S. The investigated samples were provided by K.R. Numerical simulations and writing of the paper were carried out by S.V. and C.R. All authors discussed the results and commented on the manuscript.

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Correspondence to C. Ropers.

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The authors declare no competing financial interests.

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Vogelgesang, S., Storeck, G., Horstmann, J. et al. Phase ordering of charge density waves traced by ultrafast low-energy electron diffraction. Nat. Phys. 14, 184–190 (2018).

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