Superconducting mechanism of cuprates is discussed in the light of theproximity of the Mott insulator. The proximity accompanied by suppression ofcoherence takes place in an inhomogeneous way in the momentum space infinite-dimensional systems. Studies on instabilities of metals consisted ofsuch differentiated electrons in the momentum space are reviewed from a generalpoint of view. A typical example of the differentiation is found in theflattening of the quasiparticle dispersion discovered around momenta $(\pi,0)$and $(0,\pi)$ on 2D square lattices. This flattening even controls thecriticality of the metal-insulator transition. Such differentiation andsuppressed coherence subsequently cause an instability to the superconductingstate in the second order of the strong coupling expansion. The d-wave pairinginteraction is generated from such local but kinetic processes in the absenceof disturbance from the coherent single-particle excitations. Thesuperconducting mechanism emerges from a direct kinetic origin which isconceptually different from the pairing mechanism mediated by bosonicexcitations as in magnetic, excitonic, and BCS mechanisms. Pseudogap phenomenawidely observed in the underdoped cuprates are then naturally understood fromthe mode-mode coupling of d-wave superconducting (dSC) fluctuations repulsivelycoupled with antiferromagnetic (AFM) ones. When we assume the existence of astrong d-wave channel repulsively competing with AFM fluctuations under theformation of flat and damped single-particle dispersion, we reproduce basicproperties of the pseudogap seen in the magnetic resonance, neutron scattering,angle resolved photoemission and tunneling measurements in the cuprates.
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