Spectral signature of periodic modulation and shifting of pseudogap state in moiré system

The nature of the pseudogap state is widely believed as a key to understanding the pairing mechanism underlying unconventional superconductivity. Although pseudogap states have recently been realized in moiré systems with extensive gate tunability, their local electronic structure remains largely unexplored. Here we show gate-tunable spontaneous symmetry breaking and shifting behavior of the pseudogap state in magic-angle twisted bilayer graphene using spectroscopic imaging scanning tunneling microscopy. A pronounced pseudogap emerges over a broad doping range and exhibits strong spatial modulation at the moiré scale. Spectroscopic imaging highlights a gap size modulation at moiré scale that is sensitive to the filling, indicative of a wave-like pseudogap feature. At certain dopings, the pseudogap size distribution causes a clear nematic order, or an anisotropic gap distribution. Our results have shed light on the complex nature of this pseudogap state, revealing critical insights into the phase diagram of correlated electron systems.