Introduction

The term "twistronics" — the deliberate rotation of van der Waals layers to create moiré superlattices — has graduated from a laboratory curiosity to a core platform for exploring correlated electron physics. Since the 2018 discovery that magic-angle twisted bilayer graphene (MATBG) hosts correlated insulators and superconductivity, the field has exploded. Today researchers are not only reproducing those exotic phases but extending the toolkit to transition-metal dichalcogenides (TMDs), multilayer stacks, and heterostructures that emulate Hubbard models, Chern bands and fractionalized states.

What the new generation of experiments shows

Twisting creates narrow, tunable moiré bands with quenched kinetic energy and enhanced Coulomb interactions. That simple observation underpins a string of recent results:

  • Expanded material palette: TMD heterobilayers and aligned graphene-on-hBN have produced robust correlated insulating states and magnetism, often at higher temperatures and with greater tunability than MATBG.
  • Control knobs multiply: Electric displacement fields, pressure, carrier density and interlayer bias let experimenters tune bandwidth, symmetry breaking and topology in situ — a degree of control rare in conventional correlated materials.
  • Topological and fractional phases: Moiré systems have revealed Chern insulators, orbital ferromagnetism, and signatures consistent with fractional Chern insulators, pointing to intertwined topology and strong interactions.

Why heterostructures matter

Van der Waals heterostructures are modular. By stacking different monolayers and adjusting twist angle, researchers realize model Hamiltonians with controlled bandwidth, sublattice degrees of freedom and spin–valley structure. In TMD moirés, for example, large effective masses and strong spin–orbit coupling drive Mott-like physics at one electron per moiré site, reproducing key aspects of the single-band Hubbard model but with unprecedented experimental tunability.

Debates and unresolved mechanisms

Despite progress, the field faces fundamental controversies. The dominant debate concerns the microscopic origin of superconductivity: is it driven by purely electronic correlations (analogous to cuprates), mediated by phonons, or emergent from intertwined orders such as nematicity and orbital magnetism? The answer likely varies with material, twist angle and environment. Another challenge is reproducibility: tiny angle inhomogeneities, strain and disorder can profoundly change phase diagrams, making it hard to draw universal conclusions.

Recent methodological advances

Complementary probes — high-resolution STM, nano-SQUID magnetometry, resonant transport and capacitance mapping — now allow spatially resolved glimpses into moiré physics. Theory has kept pace with continuum models, numerically exact studies of small clusters and mean-field approaches that explore competing orders. Importantly, heterostructure engineering lets theorists test specific predictions by switching off symmetries or changing interaction strengths experimentally.

Outlook

Twistronics has shifted the study of correlated electrons from an observational science to an engineering discipline: researchers can design lattices, tune interactions, and realize topological bands on demand. The next phase will require tighter control over sample homogeneity, better microscopic probes of pairing symmetry, and cross-platform comparisons that separate universal phenomenology from material-specific detail. If those hurdles are overcome, van der Waals heterostructures could provide not just analogues of known correlated phases but qualitatively new states of quantum matter — and a laboratory for testing theories that have long been speculative in bulk crystals.