We derive a $2+1$ dimensional model with unconventional supersymmetry at the boundary of an ${rm AdS}_4$ $mathcal{N}$-extended supergravity, generalizing previous results. The (unconventional) extended supersymmetry of the boundary model is instrumental in describing, within a top-down approach, the electronic properties of graphene-like 2D materials at the two Dirac points, ${bf K}$ and ${bf K}$. The two valleys correspond to the two independent sectors of the ${rm OSp}(p|2)times {rm OSp}(q|2)$ boundary model in the $p=q$ case, which are related by a parity transformation. The Semenoff and Haldane-type masses entering the corresponding Dirac equations are identified with the torsion parameters of the substrate in the model.
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