Speaker
Mr
Bart Smit
(Stellenbosch University)
Description
The 1-dimensionally conductive organic material Cu(DNCQI)2 has been a subject of interest due to its exotic macroscopic (conductivity) properties and the tuneability thereof. Depending on chemical composition, the crystal loses many orders of magnitude of conductivity within 1 K upon cooling. This phase transition is associated with a structural (‘Peierls’) transition of the (microscopic) lattice, where three crystal planes move together and form trimers. Despite the presence of a crystal lattice rearrangement, until now the only successful time resolved studies on Cu(DCNQI)2 are on macroscopic properties of the material, such as ultrafast photoinduced conductivity measurements in bulk needles. We present the first study ever on this crystal (we used Me,Br-DCNQI, Ttransition = 155 K) that reveals the microscopic molecular response on an ultrafast time scale, by using Ultrafast Electron Diffraction (UED).
The main findings of this study are the ultrafast (~2ps) full suppression of the insulating trimer phase and a full recovery thereof within ~40ps, which is one of the fastest macroscopic structural lattice phase transitions ever seen. We also observe an ultrafast change of the structure within the planes, linked to a distortion of the tetrahedral geometry of the crystal, with a slow (>ns) recovery. The successfully resolved molecular response (and the extracted ultrafast time constants) aid in understanding the underlying mechanisms of the photo-switched insulator-to-metal transition.
Level for award<br> (Hons, MSc, <br> PhD, N/A)?
PhD
Apply to be<br> considered for a student <br> award (Yes / No)?
Yes
Main supervisor (name and email)<br>and his / her institution
Prof. Dr Heinrich Schwoerer
Stellenbosch University
heso@sun.ac.za
Would you like to <br> submit a short paper <br> for the Conference <br> Proceedings (Yes / No)?
No
Primary author
Mr
Bart Smit
(Stellenbosch University)
Co-authors
Prof.
Heinrich Schwoerer
(Stellenbosch University)
Ms
Nancy Payne
(Stellenbosch University)
