Highly Asymmetric Graphene Layer Doping and Band Structure Manipulation in Rare Earth–Graphene Heterostructure by Targeted Bonding of the Intercalated Gadolinium

Heterostructures consisting of vertically stacked two-dimensional (2D)materials have recently gained large attention due to their highly controllable electronicproperties and resulting quantum phases. In contrast to the mechanically stackedmultilayered systems, which offer exceptional control over a stacking sequence or interlayertwist angles, the epitaxially grown 2D materials express unprecedented quality and stabilityover wafer-scale lengths. However, controlling the growth conditions remains a majorobstacle toward the formation of complex, epitaxial heterostructures with well-definedelectronic properties. Here, we synthesized a trilayer graphene heterostructure on theSiC(0001) substrate with two specific interlayer locations occupied by gadolinium. Weapplied multitechnique methodology based on low-temperature scanning tunnelingmicroscopy/spectroscopy (STM/S) and angle-resolved photoelectron spectroscopy(ARPES) to determine the intercalant's locations in the complex, epitaxial grapheneheterostructure. Our approach relies on very high quality and large, micrometer-scalehomogeneity of the synthesized system. The experimentally determined electronic structure is dominated by the two topmostgraphene layers. Our spectroscopic results show quantitative agreement between global ARPES, local STM/S, and density functionaltheory predictions. The characterized electronic properties primarily reflect highly anisotropic doping levels between the twocorresponding graphene layers, which significantly affect the band structure topology. Two pairs of hybridized massive Dirac bandsfrom our initial synthesisxe0d5;the bilayer graphene on the SiC(0001) substratexe0d5;are transformed upon Gd intercalation into two pairsof massless Dirac bands with a new hybridization region in between. Our results open perspectives in the realization of exotic 2Dquantum materials via atomically precise synthesis of epitaxial, multilayered graphene-rare earth heterostructures.