SIMES Seminar: Yaroslav Gerasimenko

Date(s) - Feb 14 2018
12:30 PM - 1:30 PM

Room 130, McCullough Building


Ultrafast transformation of matter: exotic metastable electronic states in 1T-TaS2 revealed with STM

Yaroslav Gerasimenko

CENN Nanocenter and Department of Complex Matter,
Jozef Stefan Institute, Ljubljana, Slovenia

Recent observation of long-living metastable states [1, 2] induced by a single ultrafast optical pulse gave access to previously unexplored area of non-stroboscopic and real space measurements for systems out of equilibrium. Here we combine in situ ultrafast optical excitation and low-temperature scanning tunneling microscopy to study both electronic and structural transformations induced in 1T-TaS2.

At low power, in the so-called hidden state [1], we observe how long range order emerges through domain phase locking in space, thus supporting the fundamental concept that macroscopic states can be created out of equilibrium [3]. Scanning the boundary of switched area clearly shows distinct electron orbital reconstruction as a part of the transition. Pushing power further gives rise to the amorphous state where a part of electrons is localized in a random pattern on the ordered atomic lattice, while another is delocalized and contributes to the state becoming metallic. Relaxation tracked by continuous scanning at 4K demonstrates that in hidden state domain wall crossing rules are important for stability. The amorphous state is more stable compared to hidden, and scanning at 77K reveals strongly constrained evolution of the localized electrons pattern and non-ergodic behavior.

I will discuss our understanding of the non-equilibrium of phase diagram and the mechanisms responsible for the emergence of long-range order and long lifetimes of the hidden and especially amorphous states.

[1] L. Stojchevska et al., Science 344, 177–180 (2014)

[2] J. Zhang et al., Nature Materials 15, 956 (2016)

[3] Ya. A. Gerasimenko, I. Vaskivskyi, D. Mihailovic, arXiv:1704.08149v2 (2017)