Quantum Materials - 07

Abstract

Moiré superlattices caused by a crystal orientation or lattice mismatch, emerge moiré potentials with longer periods than the lattice. The moiré miniband can cause the formation of flat band [1]. In our previous research, we find that by evaporate single or double-bilayer (BL) Sb honeycomb lattices on a Bi(111) surface grown on Si(111), we can get a moiré pattern due to a lattice mismatch between antimonene and Bi(111). Our group studied the property of the band structure by means of STM and ARPES measurement. Results showed a significant peak near Fermi level caused by saddle-point in the band structure.

So, the purpose of our research at the moment is improving the homogeneity of our sample to supply four-electrode conductivity measurements. Thereby we performed experiments to search for the best condition of moiré formation.[2] First, We changed thickness of the substrate Bi layer. It is found by STM measurement that moiré appears in a smaller period size on higher Bi thickness. Which means for thin Bi film at around 10 BL, it might appear a smaller lattice constant than that of bulk, which further affects moiré period size.

As our next experiment, to clearly figure out the thickness dependence of moiré pattern, we designed a experiment using mask to evaporate Bi on Si(111) substrate to get a Bi thickness gradation structure (Fig.1). The result shows that moiré crystallinity doesn’t depend much on substrate thickness.

In our latest experiment, to obtain a moiré pattern with improved crystallinity, we grew Sb on a Bi substrate at an ultra-low temperature of approximately 100 K. By freezing the Bi substrate, Sb was able to form a well-ordered atomic lattice structure. The result was quite ideal—the moiré pattern appeared more stable compared to the room-temperature case. With better periodicity over a large scale, we expect it to exhibit distinct behavior in transport experiments.