Sergey Artyukhin: Phase transition dynamics and sliding domain walls in ferroelectrics

Recent advances in scanning impedance microscopy made possible to map lattice vibrations on nanoscale and identify domain-wall localized phonons and their contribution to dielectric anomalies. Lowest energy modes are excited when the field favors one of the domains across the wall. However, 71o domain walls in BiFeO3 were found to defy this condition. Symmetry breaking at the surface and wall tilting along with interactions of the ferroelectric polarization with strains are shown to be responsible for this peculiar behavior. In addition, the soft domain wall-localized modes and surrounding long-ranged strain textures can lead to dramatic mechanic softening of the material. The second part of the talk focuses on ultrafast phase transitions related to melting and reconstruction of dimers in IrTe2 and the spin density wave in Cr. These phase transitions can be triggered by laser pulses, and interactions between electronic and lattice degrees of freedom can be studied on their natural timescales.