Miloš Borovšak, 17.05.2017 at 13:00, Seminar room F7

Phase changes in molybdenum oxides induced by AFM tip and laser excitation

Miloš Borovšak
Faculty of Mathematics and Physics, Ljubljana


Molybdenum oxides show many physical properties, especially electronic, that are similar to the physical properties of 1T-TaS2, where a phase transition from insulator to metal can occur with a single ultrashort laser pulse, and as such are very promising candidates for study, if it is possible to induce phase transitions in the material. With the use of biased tip on an atomic force microscope we were able to induce a topotactic changes at the surface of η –Mo4O11 crystals. We showed that we can influence the surface potential while the topography remains the same. We performed systematic study of femtosecond time-resolved optical spectroscopy on both molybdenum oxides. In the case of η –Mo4O11 we observed a remarkable slowing down of the relaxation dynamics at the first charge density wave transition at TCDW1 = 105 K associated with hidden one-dimensional Fermi surface nesting. We also observed that with higher fluences we induce a dynamical phase transition that cannot be explained by heating. In the case of Mo8O23 we performed some additional characterization measurements such as resistivity and Raman spectroscopy in search for CDW phase transitions but we did not observe any specific indication of it. In comparison to η –Mo4O11 we did not observe any remarkable slowing down in dynamics. We observed that the relaxation dynamics parameters have qualitatively similar behavior as the resistivity with a peak/dip structure at around 150 K.