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Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetals, and 3D node-line semimetals (NLSs). In particular, several compounds (e.g., certain 3D graphene networks, CuPdN, CaP) were discovered to be 3D NLSs, in which the conduction and valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional (2D) Dirac semimetal (e.g., graphene), 2D topological semimetals are much less investigated. Here we propose a new concept of a 2D NLS and suggest that this state could be realized in a new mixed lattice (named as HK lattice) composed by Kagome and honeycomb lattices. It is found that AB(A is a group-IIB cation and B is a group-VA anion) compounds (such as HgAs) with the HK lattice are 2D NLSs due to the band inversion between the cation Hg-s orbital and the anion As-orbital with respect to the mirror symmetry. Since the band inversion occurs between two bands with the same parity, this peculiar 2D NLS could be used as transparent conductors. In the presence of buckling or spin-orbit coupling, the 2D NLS state may turn into a 2D Dirac semimetal state or a 2D topological crystalline insulating state. Since the band gap opening due to buckling or spin-orbit coupling is small, HgAswith the HK lattice can still be regarded as a 2D NLS at room temperature. Our work suggests a new route to design topological materials without involving states with opposite parities. [ABSTRACT FROM AUTHOR]

We investigate the evolutionary prisoner's dilemma game (PDG) on weighted Newman-Watts (NW) networks. In weighted NW networks, the link weight wij is assigned to the link between the nodes i and j as: wij = (ki * kj)b, where ki(kj) is the degree of node i(j) and b represents the strength of the correlations. Obviously, the link weight can be tuned by only one parameter b. We focus on the cooperative behavior and wealth distribution in the system. Simulation results show that the cooperator frequency is promoted by a large range of b and there is a minimal cooperation frequency around b = - 1. Moreover, we also employ the Gini coefficient to study the wealth distribution in the population. Numerical results show that the Gini coefficient reaches its minimum when b [?] - 1. Our work may be helpful in understanding the emergence of cooperation and unequal wealth distribution in society. [ABSTRACT FROM AUTHOR]