Reconfigurable edge-state engineering in graphene using LaAlO3/SrTiO3 nanostructures

Abstract

The properties of graphene depend sensitively on doping with respect to the charge-neutrality point (CNP). Tuning the CNP usually requires electrical gating or chemical doping. Here, we describe a technique to reversibly control the CNP in graphene with nanoscale precision, utilizing LaAlO3/SrTiO3 (LAO/STO) heterostructures and conductive atomic force microscope (c-AFM) lithography. The local electron density and resulting conductivity of the LAO/STO interface can be patterned with a conductive AFM tip [Cen et al., Nat. Mater. 7, 298 (2008)] and placed within two nanometers of an active graphene device [Huang et al., APL Mater. 3, 062502 (2015)]. The proximal LAO/STO nanostructures shift the position of graphene CNP by ∼1012 cm−2 and are also gateable. Here, we use this effect to create reconfigurable edge states in graphene, which are probed using the quantum Hall effect. Quantized resistance plateaus at h/e2 and h/3e2 are observed in a split Hall device, demonstrating edge transport along the c-AFM written edge that depends on the polarity of both the magnetic field and direction of currents. This technique can be readily extended to other device geometries.

Gate-Tunable Optical Nonlinearities and Extinction in Graphene/LaAlO3/SrTiO3 Nanostructures

“…While it is true that a slight shift of the graphene CNP occurs due to LAO/STO patterning, the resultant change in carrier density (∆𝑛 = 7 × 10 11 cm −2 ) 22 is negligible compared to the effects of the biased nanojunction on the chemical potential. For 𝑉 𝑆𝐷 = 1 V, we estimate a change in carrier density of ∆𝑛 = 2.8 × 10 13 cm −2 and a corresponding chemical potential change of ∆𝜇 = ℏ𝑣 𝐹 √𝜋∆𝑛 = 0.62 eV.…”

“…The observed gate-tunable strong graphene-light interaction and nonlinear optical response are of fundamental interest and open the way for future exploitation in graphene-based optical devices.Because graphene typically lacks a plasmonic response in the VIS-NIR regime, such behavior is difficult to achieve at higher frequencies 13 . However, the interaction between graphene and VIS-NIR light can be enhanced by creating graphene-based metamaterials or surfaces in which the CNP is modulated at the nanoscale, for example, using AFM 14 or STM 15 , by creating arrays of graphene nanodisks or nanoribbons [10][11][12]16 , or by placing graphene near plasmonic metasurfaces or nanoscale metal gratings [17][18][19][20] .Recently, a technique to control the CNP of graphene-both reversibly and locally-has been developed using graphene integrated with LaAlO3/SrTiO3 (LAO/STO) heterostructures 21,22 . LAO/STO has a tunable conductive interface 23 with a variety of interesting physical properties 24 .…”

“…When the LAO thickness is close to the critical thickness for a metal-insulator transition, ∼3-4 unit cells 25 , the conductivity of the LAO/STO interface can be controlled using conductive atomic force microscope (c-AFM) lithography 14,26 .A wide range of optoelectronic devices can be fabricated at the LAO/STO interface in this fashion, such as a 10 nm-scale photodetector 27 and nanoscale, terahertz (THz) sources and detectors 28,29 with a bandwidth of more than 100 THz. LAO/STO nanostructures can be placed within two nanometers of an active graphene device and used, for example, to create reconfigurable edge channels in graphene 22 .…”

“…Recently, a technique to control the CNP of graphene-both reversibly and locally-has been developed using graphene integrated with LaAlO3/SrTiO3 (LAO/STO) heterostructures 21,22 . LAO/STO has a tunable conductive interface 23 with a variety of interesting physical properties 24 .…”

“…A wide range of optoelectronic devices can be fabricated at the LAO/STO interface in this fashion, such as a 10 nm-scale photodetector 27 and nanoscale, terahertz (THz) sources and detectors 28,29 with a bandwidth of more than 100 THz. LAO/STO nanostructures can be placed within two nanometers of an active graphene device and used, for example, to create reconfigurable edge channels in graphene 22 .…”