Soft-mode driven polarity reversal in ferroelectrics mapped by ultrafast x-ray diffraction
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Date
2018
Volume
5
Issue
2
Journal
Structural Dynamics
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Publisher
Melville, NY : AIP Publishing LLC
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Abstract
Quantum theory has linked microscopic currents and macroscopic polarizations of ferroelectrics, but the interplay of lattice excitations and charge dynamics on atomic length and time scales is an open problem. Upon phonon excitation in the prototypical ferroelectric ammonium sulfate [(NH4)2SO4], we determine transient charge density maps by femtosecond x-ray diffraction. A newly discovered low frequency-mode with a 3 ps period and sub-picometer amplitudes induces periodic charge relocations over some 100 pm, a hallmark of soft-mode behavior. The transient charge density allows for deriving the macroscopic polarization, showing a periodic reversal of polarity.
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CC BY 4.0 Unported