= Fermionic Bogoliubov quasiparticle
{title2=$E_{\mathbf k}=\sqrt{\xi_{\mathbf k}^2+|\Delta|^2}$}
A fermionic excitation obtained by a canonical particle–hole <Bogoliubov transformation> of a paired mean-field <Hamiltonian>. The uniform spin-singlet problem has the displayed positive <energy> and weights $|u|^2=(1+\xi/E)/2$, $|v|^2=(1-\xi/E)/2$. It interpolates between particle-like and hole-like excitations across the Fermi surface. These single-particle excitations differ from collective phase and <amplitude modes> of the <order parameter>.
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