Ultrafast large-amplitude relocation of electronic charge in ionic crystals.
basic_science · Level V
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- Record sourced from PubMed, PMID 22431621.
- Also identified by DOI 10.1073/pnas.1108206109 and PMC identifier 3325693.
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Abstract
The interplay of vibrational motion and electronic charge relocation in an ionic hydrogen-bonded crystal is mapped by X-ray powder diffraction with a 100 fs time resolution. Photoexcitation of the prototype material KH(2)PO(4) induces coherent low-frequency motions of the PO(4) tetrahedra in the electronically excited state of the crystal while the average atomic positions remain unchanged. Time-dependent maps of electron density derived from the diffraction data demonstrate an oscillatory relocation of electronic charge with a spatial amplitude two orders of magnitude larger than the underlying vibrational lattice motions. Coherent longitudinal optical and tranverse optical phonon motions that dephase on a time scale of several picoseconds, drive the charge relocation, similar to a soft (transverse optical) mode driven phase transition between the ferro- and paraelectric phase of KH(2)PO(4).