Abstract
We propose a new principle to realize flatbands which are robust in real materials, based on a network superstructure of one-dimensional segments. This mechanism is naturally realized in the nearly commensurate charge-density wave of 1T-TaS_{2} with the honeycomb network of conducting domain walls, and the resulting flatband can naturally explain the enhanced superconductivity. We also show that corner states, which are a hallmark of the higher-order topological insulators, appear in the network superstructure.
Highlights
We propose a new principle to realize flatbands which are robust in real materials, based on a network superstructure of one-dimensional segments
We argue that this mechanism is naturally realized in the nearly commensurate chargedensity wave (NC-CDW) phase of 1T-TaS2, in which the domain walls play the role of the one-dimensional metallic segments [8]
The robust flatbands ensured by the new principle give a natural explanation of the observed superconductivity, which is strongly reminiscent of the moirephysics [5,6,7] of twisted bilayer graphene
Summary
Having established the stability of the flatbands, we discuss the many-body physics when the Fermi level is near one of the flatbands. It is well known that the coupling of electrons and (optical or gapped) phonons effectively plays the same role as the attractive U, which favors the s-wave SC [22]. When the repulsive-U dominates the junction region and the region becomes Mott insulating [58], J > 0 can appear From this strong-coupling limit, we can learn how the 2kF-density wave of 1D wires competing with SC is suppressed. For the generic filling of each wire, the momentum kF will not be commensurate with the wire length L, i.e., φL 1⁄4 kFL is not a rational number This frustrates the phases of the density waves and their true two-dimensional order is strongly suppressed to develop. These suggest that the SC state of 1T-TaS2 is likely an s-wave SC
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