Selected results of department 12

Unusual behaviour of new cholesteric liquid crystals has been observed under applied electric field. Positive dielectric anisotropy causes reorientation of the long molecular axis along the applied electric field direction. Due to extremely short pitch length a stripe texture has been observed under applied electric field. A model based on disclinations has been proposed and anchoring energy evaluated.

Ultrashort laser pulses can be used to induce transient exotic states of matter and cause phenomena of a vital interest such as room temperature superconductivity. We have focused on the photo-induced dynamics in niobium nitride (NbN) thin films [1] under strong excitation.

The structural ferroelectric-paraelectric transition has been observed by electron diffraction tomography in the tetragonal tungsten-bronze (TTB) Sr_0.35Ba_0.61Nb₂O_6.04 (SBN-35). The combination of structural and broad-band dielectric studies in SBN-35 suggests that ferroelectricity in TTBs in caused by a more complex mechanism than in perovskites.

The high-frequency dielectric response of the uniaxial strontium barium niobate (Sr_xBa_1−xNb₂O₆) crystals with 81% of Sr (x = 0.81) was studied from 1 kHz to 30 THz along the polar axis in a wide temperature interval [E. Buixaderas et al, Sci. Rep. 7, 18034 (2017)]. Relaxor properties were observed in the complex dielectric response and four main excitations were ascertained below the phonon frequencies. These fast polarization mechanisms take place at THz, GHz and MHz ranges and show different temperature evolution.