Winding number of a one-dimensional Bogoliubov--de Gennes Hamiltonian
= Winding number of a one-dimensional Bogoliubov--de Gennes Hamiltonian
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For a two-component gapped BdG Hamiltonian constrained to a plane, the winding number counts how many times its coefficient vector encircles the origin as crystal momentum traverses the Brillouin zone.