critical temperature magnetic field superconductors superconducting superconductivity theory of superconductivity Meissner effect electrons energy electrical current theory superconducting state temperatures BCS theory the resistance Tc superconductor Type II Ba oxygen planes atoms Hg compound physicists resistance electron oxygen atoms Ginzburg-Landau theory Tl phenomenon metal liquid nitrogen history of superconductivity high-temperature superconductors layers conductor interaction pairs voltage Cooper pairs real metal Brookhaven National Laboratory Cooper pair transition temperature Meisner effect High-temperature Superconductivity the normal conduction electrons energy gap mass Quantum Physics orbits exhibit condensation lattice vibrations interactions explanation stone mechanism superconductivity research electrical resistance high temperature superconductors rings Introduction to superconductivity high-temperature superconductor conventional superconductors Wikinfo Superconductivity concepts metals the fluid resistivity conventional superconductor History of superconductivity number of electrons discovery helium alloys superconducting phase the London vortices magnet lattice fluid New World Encyclopedia John Bardeen currents Type-II superconductors Nave magnetic fields Superconductivity TC superconductivity experiments PhysOrg high-temperature superconductivity Physics unit cell electricity iron arsenide evidence research National Institute of Standards and Technology Physics News Japanese scientists high-Tc superconductors electron pairs phonon encounters specific heat frac mathbf electrical resistivity psi flux researchers phonons Meissner Effect math cuprate superconductors