Microscopic Theory of Novel Pseudogap Phenomena and Bose-Liquid Superconductivity and Superfluidity in High-Tc Materials and Other Systems

A predictive and empirically adequate microscopic theory of novel pseudogap phenomena and Bose-liquid superconductivity and superfluidity in high-T c materials and other systems is presented. This theory predicts new fundamental results and laws in physics. These new findings indicate that (i) the pseudogap state and bosonic Cooper pairs are formed above the superconducting/superfluid transition temperature T c in the systems with low Fermi energy ε F ~ε A (where ε A is the energy of the attractive interaction between fermionic quasiparticles), (ii) only a minority of such Cooper pairs condenses into a Bose superfluid and the superconducting/superfluid order parameter (as distinct from theBCS-like gap) appears below T c , (iii) new types of condensation of attracting bosons give rise to two distinct superconducting/superfluid phases below T c , and (iv) the unusualsuperconducting/superfluid state and λ-like phase transition in pseudogap systems are similar to those in liquid 4 He. The constructed theory is capable of explaining all the unusual superconducting/superfluid and normal-state properties of various substances. In particular, in high-T c cuprates, unconventional electron-phonon interactions and polaronic effects give rise to in-gap states, Fermi-surface reconstruction, two distinct pseudogaps and unusual normal-state properties, a quantum critical point in the overdoped region and a crossover from BCS superconductivity to Bose-liquid superconductivity. The criteria for bosonization of Cooper pairs and the new laws of condensation of attracting bosons are formulated. The theory of three-dimensional (3D) and two-dimensional (2D) Bose superfluids describes fairly well the novel superconducting states (i.e., so-called A and B phases below T c and a vortex-like state above T c ) and properties (e.g., λ-like transition at T c , first-order phase transition at lower temperatures and other unusual features) of high-T c cuprates in accordance with the experimental data. The present theory predicts that 2D Bose-liquid superconductivity above the bulk T c can be realized in alternating 3D non-superconducting/2Dsuperconducting sandwich layers (e.g., at grain boundaries and interfaces) in new specially-grown-specimens of high-T c cuprates at room temperature, while 3D Bose liquid superconductivity can occur at room temperature in other high-T c materials (e.g., in high-T c hydrides H 3 , LaH 10 and C-S-H) under high pressures. Superconducting/superfluid states and properties of heavy-fermion and organic compounds, ruthenate Sr 2 RuO 4 and possibly high-T c hydrides, quantum liquids ( 3 He and 4 He) and atomic Fermi gases are also well explained by the proposed theory of Bose superfluids. Finally, new criteria and principles of unconventional superconductivity and superfluidity are formulated.