Electronic Amorphous State of 1T-TaS2: ‌An Order Embedded in the Disorder

Y. Vaskivskyi,1,2 P. Aupic,2 J. Vodeb,1 Q. Hu,1 F. Scepanovic,2 D. Mihailovic1,2,3

1Department of Complex Matter, Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia

2Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia

3CENN Nanocenter, Jamova 39, SI-1000 Ljubljana, Slovenia

The 1T-TaS2, a peculiar transition metal dichalcogenide with a charge density wave (CDW) at low temperatures, has been studied for the last 10 years since the original discovery of a metastable hidden (H) state in it [1]. Mainly, the research was focused on the properties of this state [2] as well as their possible applications [3]. The H-state can be achieved by driving the material out of equilibrium using an ultrashort laser pulse or a short electrical pulse. Similarly to the H-state, at higher excitation fluences an electronic amorphous (A) state can be reached.

In our scanning tunnelling microscopy studies, we are exploring the coexistence of amorphous, commensurate (C) and hidden CDWs; and the dynamical reconfigurations between them. At the same time, we are showing that in addition to these CDWs, the A-state can locally form embedded `islands` of charge order not observed in any other states of the material. In addition, studies of the dynamics in the A-state are showing possible transitions as well as thermal fluctuations of this ordering.

The observed local behaviour of this system with various emergent states is a good example of topologically-constrained dynamics. As a result, the A-state of 1T-TaS2 provides valuable insight into the correlation between topology and kinetics in many-body quantum states and can be considered an accessible experimental model for studying non-equilibrium quantum dynamics.

Fig. 1. A-state of 1T-TaS2 measured with STM with a high (a) and normal (c) CDW density. a, c) Positions of the CDW peaks (points) and corresponding Voronoi tessellations (filled polygons). The colourmap is defined by Na/p – the number of atomic positions occupied by a single peak of CDW with red corresponding to the most dense CDW order. Na/p=13 corresponds to the commensurate CDW in 1T-TaS2. b, d) Original STM images showing the border between the A and the H states.

1. L. Stojchevska et al. Science 344, 177–180 (2014)
2. I. Vaskivskyi et al. Sci. Advances 1, e1500168 (2015)
3. A. Mraz et al. Nano Lett. 22, 4814-4821 (2022)