Layered van der Waals (vdW) materials are emerging as one of the most versatile directions in the field of quantum condensed matter physics. They allow an unprecedented control of electronic properties via stacking of different types of two-dimensional (2D) materials [1,2] and, moreover, by tuning the relative angle between them [3,4]. A fascinating frontier, largely unexplored, is the stacking of strongly-correlated phases of matter in vdW materials. Here, we study 4Hb-TaS 2 , which naturally realizes an alternating stacking of a Mott insulator, recently reported as a gapless spin-liquid candidate(1T-TaS 2 ) [5,6], and a 2D superconductor competing with charge-density wave order (1H-TaS 2 ) [7]. This raises the question of how these two components affect each other. We find a superconducting ground state with a transition temperature of 2.7K, which is significantly elevated compared to the 2H polytype (Tc=0.7K). Strikingly, the superconducting state exhibits signatures of timereversal-symmetry breaking abruptly appearing at the superconducting transition, which can be naturally explained by a chiral superconducting state.Chiral superconductors (SCs) have received much attention in recent years as a promising platform for hosting Majorana bound states in the vortex cores or at sample edges due to the topological nature of their ground states [8,9]. In 2D, chiral superconductors are characterized by a Chern number. The Majorana bound states are predicted to possess non-Abelian statistics, which makes them candidates for performing fault-tolerant quantum computations [10]. The order parameter of these chiral states break time-reversal symmetry (TRS), which manifests itself at edges and defects [11] and can be detected with probes such as muon spin relaxation and polar Kerr effect.Of all the known superconductors, only few exhibit signatures of TRS breaking, and even fewer are candidates for this elusive chiral phase. The best known among them are the spin-triplet superconductors Sr 2 RuO 4 , believed to be of p + ip symmetry [12] and UPt 3 [13], a potential f + if superconductor, as well as the spin-singlet heavy-fermion superconductors URu 2 Si 2 [14] and SrPtAs [15,16], which were suggested to be of d + id symmetry. Open questions remain, however, in all cases [17,18].In this work, we show evidence for chiral superconductivity in the transition-metal dichalcogenide (TMD) 4Hb-TaS 2 . We show that this polymorph of TaS 2 is a superconductor with a relatively high T c , anomalous transport properties and that it exhibits a spontaneous appearance of magnetic moments with the onset of superconductivity.4Hb-TaS 2 belongs to the P 63/mmc hexagonal space group, with a unit cell that consists of alternating layers of 1H-TaS 2 (half of 2H-TaS 2 ) and 1T-TaS 2 , see Fig. 1(a). The overall crystal is inversion symmetric, with the inversion point lying in the center of the 1T layer. The weak interlayer coupling allows to describe 4Hb-TaS 2 as a stack of 2D monolayers: 1H-TaS S with a locally broken inversion symmetry giving r...
