Berlin 2015 – scientific programme
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O: Fachverband Oberflächenphysik
O 77: Focus Session: Structural Dynamics in Nanoscale Materials Probed by Ultrashort Electron Pulses
O 77.4: Talk
Thursday, March 19, 2015, 12:00–12:15, MA 005
Ultrafast metamorphosis of a complex charge-density wave — Kerstin Haupt1, Maximilian Eichberger2, Nicolas Erasmus1, Andrea Berenike Rohwer1, Jure Demsar3, Kai Rossnagel4, and •Heinrich Schwoerer1 — 1Stellenbosch University, Stellenbosch 7600, South Afrika — 2University of Konstanz, 78457 Konstanz, Germany — 3University of Mainz, 55128 Mainz, Germany — 4University of Kiel, 24098 Kiel, Germany
The transitions between commensurately and incommensurately modulated crystalline phases generally involve the formation and rearrangement of domain walls (discommensurations) and is thus thought to be extremely slow. Here, using ultrafast electron diffraction, we directly observe the structural dynamics of a photo-induced transition between a nearly commensurate and an incommensurate charge-density-wave phase in the strongly correlated layer compound 1T-TaS2. The formation of the incommensurate phase is found to proceed in two steps, an ultrafast (≈1 ps) nucleation and a slower, thermally activated growth of domains. The transition can be fully completed in ≈100 ps, orders of magnitude faster than previously observed for commensurate-to-incommensurate transitions. The mechanism and time scales of this transition may be generic for ultrafast structural transformations between complex phases in which there is no direct path via coherent excitation of specific lattice modes.