Bogoliubov-de Gennes (BdG)

bdg_hamiltonian(hamiltonian, k, ...)	Construct the BdG Hamiltonian at momentum k.
diagonalize_bdg(hamiltonian, kgrid, ...)	Diagonalizes the BdG Hamiltonian.
gap_equation(hamiltonian, beta, ...)	Gap equation.
calculate_superfluid_weight(hamiltonian, ...)	Calculate superfluid weight (conventional + geometric).
calculate_current_density(hamiltonian, k, ...)	Calculate current density from BdG wavefunctions and normal-state Hamiltonian derivatives.