Tunable Bulk Crystal Analogues of Moiré Materials

In the past decade, moiré materials have revolutionized how we engineer and control quantum phases of matter. They are versatile platforms for strongly correlated electronic phenomena and support novel ferroelectric, magnetic, and superconducting states. Among incommensurate materials, moiré materials are aperiodic composite crystals whose long-wavelength moiré superlattices enable tunable properties without chemically modifying their component layers. To date, nearly all reports of moiré materials have investigated van der Waals heterostructures assembled far from thermodynamic equilibrium. In this talk, we introduce a conceptually new approach to synthesizing high-mobility moiré materials in thermodynamic equilibrium. We report a new family of foliated superlattice materials (Sr6TaS8)1+δ(TaS2)8 that are exfoliatable van der Waals crystals with atomically incommensurate lattices. Lattice mismatches between alternating layers generate moiré superlattices, analogous to those of 2D moiré heterobilayers, that are coherent throughout these crystals and are tunable through their synthesis conditions without altering their chemical composition. Using transport and thermodynamic measurement techniques, we uncover a rich landscape of tunable quantum material properties derived from the distinctive lattice structure of these bulk moiré metals, including signatures of a complex spectrum of quantum oscillation frequencies that are most naturally described under a higher-dimensional (4D) superspace theoretical framework. More broadly, our work demonstrates a scalable synthesis approach potentially capable of producing large-area moiré materials for electronics applications and evidences a generalizable material design concept for accessing a broad range of physical phenomena proposed in higher dimensions.