Researchers used micro‑focused angle‑resolved photoemission spectroscopy (microARPES) on in‑situ gated samples to probe twisted double bilayer graphene (tDBG) with 3.1° and 6.0° twist angles. The technique maps electron energies and momenta while a gate voltage (0–12 V) tunes the electric field across the layers.

At 6.0°, the band edges of the valence and conduction bands remained unchanged relative to two separate bilayers, but the spectrum displayed electric‑field–controlled hybridisation gaps and band flattening at deeper binding energies. For the 3.1° device, the moiré superlattice altered dispersion near the band edges, producing flat bands between the valence‑band maximum of the bottom bilayer and the conduction‑band minimum of the top bilayer as the gate voltage was increased.

The 6.0° device showed a hybridisation gap that grew from roughly 180 meV to 210 meV as the gate voltage rose from 0 to 12 V, while the 3.1° device exhibited a non‑monotonic gap that increased up to about 6 V and then decreased at higher fields.

The ARPES measurements were performed at room temperature (300 K), which limits energy resolution for low‑energy states. Additionally, stray electric fields prevented the application of gate voltages above 12 V, constraining the explored field range.