Seminars Archive

Ultrafast energy transfer in a multiferroic layered organic-inorganic hybrid

Abstract
Layered Cu-based organic-inorganic hybrid materials represent a new class of multiferroics, with ferroelectric order predominantly arising from the organic constituents, and magnetic order from the inorganic counterpart. A Raman spectroscopic study, combined with DFT calculations shows that the ferroelectric phase transition of di-phenylethylaminecoppertetrachloride [(C6H5CH2CH2NH3)2CuCl4] is caused by condensation of a mixed organic-inorganic vibrational mode. As a result the large dipole organic molecules become tilted in an alternating fashion, leading to the observed polar nature of the low temperature phase. Because of the relevance of the interplay between the organic and the inorganic moieties we performed time-resolved optical measurements aimed to decouple the two systems and investigate their interaction. Decoupling is achieved by selective ultrafast excitation of the inorganic subsystem. The energy relaxation is detected by linear birefringence which allows ultrafast measurement of the temperature at different time-delays. It is observed that the thermalization process critically slows down when approaching the critical temperature from below. This observation is discussed in terms of a diverging vibrational contribution to the heat capacity. In addition, our experiments provide an elegant method to extract the vibrational coupling constant governing the energy transfer between the inorganic layers and the crystal as a whole.