Moiré patterns formed by stacking atomically-thin van der Waals (vdW) crystals can give rise to dramatic new physical properties, in select cases generating flat bands that host superconductivity, magnetism, and other strongly correlated states of matter. The study of moiré materials has so far been limited to structures comprising no more than a few vdW sheets, since a moiré pattern localized to a single two-dimensional interface is generally assumed to be incapable of appreciably modifying the properties of a bulk three-dimensional crystal. Here, I will discuss the evolution of moiré effects in graphitic structures as the thickness varies from a few layers into the bulk limit. In particular, we investigate the family of twisted M+N graphene multilayers created by stacking and rotating M- and N-layer Bernal graphene sheets. We observe correlated and topological states with striking commonalities across many different structures in the ultra-thin limit (e.g., t1+2, t2+2, t1+3, t2+3, etc), owing to a close resemblance of their moiré flat bands. We further uncover entirely new types of moiré reconstruction effects in twisted bulk graphitic structures, in which a single graphene sheet is slightly rotated atop a Bernal graphite film that is at least six layers thick (i.e., t1+Z, where Z ≥ 6). The surface moiré potential heavily modifies the electronic properties of the entire graphitic thin film, resulting in a complex evolution of the electronic transport with gating that is mediated jointly by the moiré and bulk graphite bands. The unique properties of these moiré/bulk hybrid structures derive from the semimetallic nature of graphite, establishing a new class of moiré materials with mixed dimensionality.
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