In Operando Angle‐Resolved Photoemission Spectroscopy with Nanoscale Spatial Resolution: Spatial Mapping of the Electronic Structure of Twisted Bilayer Graphene

To pinpoint the electronic and structural mechanisms that affect intrinsic and extrinsic performance limits of 2D material devices, it is of critical importance to resolve the electronic properties on the mesoscopic length scale of such devices under operating conditions. Herein, angle-resolved photoemission spectroscopy with nanoscale spatial resolution (nanoARPES) is used to map the quasiparticle electronic structure of a twisted bilayer graphene device. The dispersion and linewidth of the Dirac cones associated with top and bottom graphene layers are determined as a function of spatial position on the device under both static and operating conditions. The analysis reveals that microscopic rotational domains in the two graphene layers establish a range of twist angles from 9.8 (cid:1) to 12.7 (cid:1) . Application of current and electrostatic gating lead to strong electric fi elds with peak strengths of 0.75 V/ μ m at the rotational domain boundaries in the device. These proof-of-principle results demonstrate the potential of nanoARPES to link mesoscale structural variations with electronic states in operating device conditions and to disentangle such extrinsic factors from the intrinsic quasiparticle dispersion. the sample position using a piezoelectric manipulator and collecting the angular and energy distributions of photoemitted electrons at each spot with a Scienta Omicron DA30 hemispherical electron analyzer. The energy and angular resolution were set to 30 meV and 0.2 (cid:1) , limited by the require-ment to achieve a reasonable signal-to-noise ratio with the low photon fl ux of 10 10 photons/s caused by the use of a zone plate. The sample was held at a temperature of 70 K during the measurements.