Abstract:
Characterization and manipulation of physical properties, such as ferroelectricity and superconductivity, of complexed materials by using multi-modal approaches have deep significance in understanding the underlying physics and initiating new technologies. By using multiple probes, one can easily conceive a completer and more sophisticated picture of complexed systems by interrogating different aspects of its properties from different length scales to timescales among various degrees of freedom. To accommodate these experimental requirements, systematic integration of instrumentations with various capabilities becomes pivotal for the success of material research.

Ultrafast dynamics of ferroelectric materials with intricate coupling of various degrees of freedom in nonequilibrium state, which cannot be achieved via thermal equilibrium path, may find rich applications in memory and computational devices, in addition, it is also an ideal platform to take the multi-modal approaches into full play. In this talk, I will show two examples of employing THz-pump multi-modal-probe approaches in the investigation of the field-induced ultrafast dynamics in quantum paraelectric KTaO3 crystal and the collective excitations of ferroelectric twin-domains in PbTiO3/SrTiO3 (PTO/STO) superlattices respectively. For the KTaO3 crystal, we observed distinct relaxation time from SHG and Kerr rotation measurements respectively and we speculate that the longer one from Kerr rotation may be related to the motion of the polar nanoregions. For the non-oscillatory component in the SHG measurement, our results demonstrate an origin of hot-phonon effect instead of a signature for ferroelectric phase transition or dipolar interaction between local polar structures. In the PTO/STO superlattices, a couple of collective modes in sub-THz range are identified and categorized into two different groups by symmetry with different characteristics. The dramatic differences of sub-ps response from XFEL and SHG demonstrate the necessity of multi-modal approaches and potentially trigger new directions for future research. These work demonstrate the capability of multi-modal approaches in establishing properties of complexed materials which are coherently driven by external stimulations.