Striped electronic phases in an incommensurately modulated van der Waals superlattice

Electronic properties of crystals can be manipulated using spatially periodic modulations. Long-wavelength, incommensurate modulations are of particular interest, exemplified recently by moiré patterned van der Waals (vdW) heterostructures. Bulk vdW superlattices hosting interfaces between clean 2D layers represent scalable bulk analogs of vdW heterostructures and present a complementary venue to explore incommensurately modulated 2D states. Here we report the bulk vdW superlattice SrTa_2S_5 realizing an incommensurate 1D modulation of 2D transition metal dichalcogenide (TMD) H-TaS_2 layers. High-quality electronic transport in the H-TaS_2 layers, evidenced by quantum oscillations, is made anisotropic by the modulation and shows commensurability oscillations akin to lithographically modulated 2D systems. We also find unconventional, clean-limit superconductivity (SC) in SrTa_2S_5 with a pronounced suppression of interlayer coherence relative to intralayer coherence. Such a hierarchy can arise from pair-density wave (PDW) SC with mismatched spatial arrangement in adjacent superconducting layers. Examining the in-plane magnetic field H_ab dependence of interlayer critical current density J_c, we find anisotropy with respect to H_ab orientation: J_c is maximized (minimized) when H_ab is perpendicular (parallel) to the stripes, consistent with 1D PDW SC. From diffraction we find the structural modulation is shifted between adjacent H-TaS_2 layers, suggesting mismatched 1D PDW is seeded by the striped structure. With a high-mobility Fermi liquid in a coherently modulated structure, SrTa_2S_5 is a promising host for novel phenomena anticipated in clean, striped metals and superconductors. More broadly, SrTa_2S_5 establishes bulk vdW superlattices as macroscopic platforms to address long-standing predictions for modulated electronic phases.