Nanoscale polytype heterostructures

R. Venturini,1 Y. Vaskivskyi,1,2 Q. Hu,1 P. Aupič,1,2 D. Mihailović1,3

1Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia

2Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia

3CENN Nanocenter, Jamova 39, Ljubljana, Slovenia

The transitional metal dichalcogenides crystalize in different polytypes, dictating their charge density wave (CDW) states. It is possible to perform the polytype transformation in situ by either an optical [1] or an electrical pulse [2,3], creating new nanoscale structures and polytypes that sometimes do not exist as bulk materials. We explore the polytype transformed structures of bulk materials 2H-NbSe2 and 4Hb-TaSe2.

Using the electrical pulse from the STM tip, the surface of the 2H-NbSe2 is transformed to the 1T polytype in which we observe rich CDW physics of domains and domain walls, as well as dynamical switching between different charge ordering configurations. The diverse spectroscopic signature of the CDW state shows a similarity to the hidden state of 1T-TaS2 [4].

We also present experiments on 4Hb-TaSe2 which consists of alternating stacking of the 1T and 1H layers. Similar to the 2H-NbSe2 experiments, we show that it is possible to create a nanoscale polytype transformation of the top surface from the 1H to the 1T polytype with the electrical pulse from the STM tip. Although the transformed 1T polytype in both materials adopts the same √13×√13 CDW superlattice, their electronic structure is different. Other materials from the group of 2H and 4Hb polytypes could likely be explored for nanoscale polytype transformations.

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2. J. Zhang et al. Science 274, 757 (1996)
3. F. Bischoff et al. Chem. Mater. 29, 9907 (2017)
4. D. Cho et al. Nat. Commun. 7, 10453 (2016)