Heterostructure

Synergetic behaviors in heterostructures composed of 2D van der Waals materials and transition metal oxides (TMO) have attracted a lot of interest. However, difficulties to fabricate high-quality graphene and SrTiO₃ (STO) heterostructure has largely prevented from observing the combined phenomena, despite the intrinsically intriguing properties such as quantum Hall effect and large dielectric constant of each constituent. In this study, we successfully observed the quantum conductance behavior of monolayer graphene on epitaxial STO thin film grown on Nb-doped STO single-crystalline substrate. Our device shows a narrow gate voltage sweep range compared to similar devices on a silicon substrates owing to the high-k nature of STO [1]. In addition, oxygen vacancies in the STO layer could be controlled by applying a wider range of gate-voltage, resulting in a systematic development of hysteresis of conductance on top of quantum Hall nature [2]. Considering the generation and annihilation of oxygen vacancies by electric field, we could construct a simple mechanism to figure out the hysteresis and a quantitative relationship among the dielectric properties of STO with oxygen vacancies.
[1] Park, J. et al., Nano Lett. 16, 1754 (2016).
[2] K. T. Kang. et al., Adv. Mater. 29, 1700071 (2017).