On Realization of the Bose-Einstein Condensates and Quantum Superfluids |

T. Domański
Institute of Physics, M. Curie-Skłodowska University, pl. M. Curie-Skłodowskiej 1, 20-031 Lublin, Poland |

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The purpose of this work is twofold. In the first part we describe superfluidity/superconductivity as an emergent phenomenon resulting from two body correlations in presence of the Bose-Einstein condensation of particles. We briefly discuss the underlying mechanism for bosons as well as fermion pairs and illustrate various realizations of superfluidity emphasizing the recent examples. In the second part we study the glassy liquid of incoherent pairs which might exist above the transition temperature T_{c} in the underdoped regime of cuprate superconductors. In particular, we explore the angular variation of pseudogap within two dimensional version: of the boson fermion model using for a quantitative analysis the projective method. We find that above T_{c} the pseudogap closes first near the nodal areas restoring there pieces (arcs) of the Fermi surface whereas remaining parts of the large Fermi surface around the antinodal points are still absent due to incoherent pairs. Upon increasing temperature the length of the Fermi arcs enlarges because the superconducting correlations are gradually suppressed. An intriguing death of Fermi surface can thus be closely related to the Bogoliubov quasiparticles whose existence in the pseudogap state has been predicted by us and confirmed recently by the angle resolved photoemission spectroscopy measurements on Bi_{2}Sr_{2}CaCu_{2}O_{8} and La_{1.895}Sr_{0.105}CuO_{4} compounds. |

DOI: 10.12693/APhysPolA.118.204 PACS numbers: 74.20.-z, 74.20.Mn, 74.40.-n |