The Magnetic Origin of dx2-y2 High-Tc Superconductivity from Tunneling Spectroscopy Measurements on Bi2Sr2CaCu2O8+x Single Crystals

The complete scenario of high-Tc superconductivity based on experimental data from electron-tunneling spectroscopy on underdoped, overdoped and Ni-doped Bi2Sr2CaCu2O8+x single crystals using a break-junction technique is presented. There are two different types of superconductivity in cuprates: superconductivity due to pairing of spinons on charged stripes and magnetic superconductivity mediated by spin-waves. The coherent state of the spinon superconductivity is established via the magnetic superconductivity. In Nd2-xCexCuO4, there is only the spinon superconductivity and the coherent state is established due to the Josephson coupling between charged stripes. Below Tc, we observe four different gaps, namely, (i) a SDW gap due to antiferromagnetic correlations; (ii) a superconducting gap due to spinon pairing; (iii) a d-wave magnetic superconducting gap, and (iv) a small superconducting gap most likely having gwave symmetry. We show that the d-wave superconductivity is mediated by spin-waves and the magnitude of the superconducting gap due to pairing of spinons is larger than the magnitude of the d-wave gap, however, the d-wave gap is more intense. The superconducting gap due to pairing of spinons most likely has a s-wave symmetry. The maximum magnitudes of the SDW, the spinon and d-wave gaps are located at (π/2, π/2), (π/2, π/2) and (π, 0) on the Fermi surface, respectively. The d-g-wave superconductivity mediated by spin-waves can be considered as a pairing of magnetic polarons. We formulate a theorem for cuprates by analogy with the Anderson's theorem for classical superconductors. The presented model of high-Tc superconductivity naturally explains other experimental data. PACS. 74.20.Mn Nonconventional mechanisms 74.50.+r Tunneling phenomena 74.72.Hs Bi-based cuprates