Visualizing the Effect of an Electrostatic Gate with Angle-Resolved Photoemission Spectroscopy

Abstract

Electrostatic gating is pervasive in materials science, yet its effects on the electronic band structure of materials has never been revealed directly by angle-resolved photoemission spectroscopy (ARPES), the technique of choice to non-invasively probe the electronic band structure of a material. By means of a state-of-the-art ARPES setup with sub-micron spatial resolution, we have investigated a heterostructure composed of Bernal-stacked bilayer graphene (BLG) on hexagonal boron nitride and deposited on a graphite flake. By voltage biasing the latter, the electric field effect is directly visualized on the valence band as well as on the carbon 1s core level of BLG. The band gap opening of BLG submitted to a transverse electric field is discussed and the importance of intralayer screening is put forward. Our results pave the way for new studies that will use momentum-resolved electronic structure information to gain insight on the physics of materials submitted to the electric field effect.

Electronic structure of 2D van der Waals crystals and heterostructures investigated by spatially- and angle-resolved photoemission

“…At high gate fields, Nguyen et al could also populate the Q valley in WSe 2 and demonstrate directly that its energy is slightly above the conduction band minimum at K. They further showed that this situation reverses in bi-and trilayer WSe 2 where the Q valley dips below the K valley, resulting in an indirect gap, consistent with prior results from optics [17]. Near simultaneous with the work of Nguyen et al, Joucken et al demonstrated in situ electrostatic gating of Bernal bilayer graphene during ARPES measurements [132]. Subsequently, in-operando ARPES studies have also been reported on monolayer graphene [133][134][135] and bilayer graphene with large twist angle [136,137].…”

Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES

“…Similar approaches have only recently been demonstrated to lead to electrostatically tunable bands in single-layer graphene [32,33] and Bernal-stacked bilayer graphene. [34] An optical micrograph of the device is compared to a map of the photoemission intensity in Figure 1b,c, revealing the location of the twBLG flake between the top contacts used for grounding the flake. The data underlying the nanoARPES map is composed from a 4D dataset containing the (E, k, x, y)-dependent photoemission intensity and the image merely represents a projection of the E-and k-integrated intensity onto real space.…”

Momentum-resolved view of highly tunable many-body effects in a graphene/hBN field-effect device

“…The mesoscopic sizes and intrinsic inhomogeneities of such devices have posed the biggest challenges precluding conventional ARPES studies. These issues can be circumvented by using a microscopically focused beam of photons as demonstrated in recent microARPES experiments performed on 2D material based heterostructures and devices [20][21][22][23]. We apply this approach here to investigate the Coulomb interaction in graphene on hBN (graphene/hBN) at a relatively small interlayer twist angle of 2.0 • .…”