PetrinaD. Ya. “New Second Branch of the Spectrum of the BCS Hamiltonian and a ‘pseudogap’”. Ukrains’kyi Matematychnyi Zhurnal 57, no. 11 (November 25, 2005): 1508–1533. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3704.