Studies Of The Quantum Transport Properties And Interlayer Interactions In The Hybrid System Composed Of Graphene And LaAlO₃/SrTiO₃

Graphene and LaAlO3/SrTiO3 heterointerface are two representative two dimensional electronic systems with abundant physical properties that can be readily tuned by the electric field.Due to the surface-sensitive nature of graphene and LaAlO3/SrTiO3,the hybrid system composed of such two distinct materials offers an excellent opportunity to optimize functionalities and exploit intriguing properties through proximal coupling.In addition,the interlayer interactions between such two distinct systems will also be quite appealing.In this thesis,such hybrid systems were successfully fabricated,and the quanum transport properties of graphene,as well as the interlayer interactions between graphene and LaAlO3/SrTiO3,were investigated.The main results are as follows:1.Studies of the substantially enhanced robustness of quantum Hall effects in graphene on LaAlO3/SrTiO3 heterostructure.By exploiting 5 uc LaAlO3 as a natural bottom-gate dielectric layer,an ultra-large gate capacitance of up to 1.59?F/cm2 was obtained,which enables significantly reduced operating gate-voltage for the graphene-based field-effect device.Moreover,well-defined quantum Hall effects were realized at relatively modest conditions,for example,at 1.5 K/1.5 T,and 150 K/7 T.The substantially enhanced robustness is attributed to the effective suppression of multiple scattering processes in the graphene layer with the help of LaAlO3/SrTiO3.These results make such a hybrid structure a viable choice for the development of graphene-based quantum resistance metrology at low magnetic fields and elevated temperatures.2.Studies of giant-capacitance-induced wide quantum Hall plateau phenomena.In graphene on LaAlO3/SrTiO3 heterostructure,quantum Hall plateaus at filling factors v=±2 were successfully realized over a wide range of the magnetic field and gate-voltage,for example,extending from 2 T to a maximum available field of 9 T.Through analyzing via a simple band diagram model,the wide Hall plateaus are revealed to arise from the ultra-large capacitance of the ultra-thin LaAlO3 layer acting as the dielectric layer,rather than the charge transfer relying on interface states.Such a novel route may be further utilized to optimize the quantum transport performance of graphene and more generalized 2D material systems.3.Studies of the supercurrent drag effect between graphene and the superconducting LaAlO3/SrTiO3 interface.While applying a drive current in graphene layer,a negative drag voltage was induced at the LaAlO3/SrTiO3 interface only in the vicinity of the superconducting transition.The high tunability of both layers and the ultra-small interlayer spacing lead to a giant interlayer coupling ratio up to 50 in the zero-temperature limit.As a consequence,this effect may find its applications in the development of novel superconducting electronic devices.Moreover,the revealed evolution behaviors under multiple external fields,especially the novel carrier density/polarity and temperature dependencies,point to a brand-new microscopic mechanism.Our study will inspire further exploration of hybrid interlayer coupling via utilizing newly-emerging two-dimensional electronic systems,in particular the ones possessing long-range order.