At low temperatures, substances can be electrical conductors {superconductor} with no electrical resistance {superconductivity}|. Liquid oxygen, liquid nitrogen, and liquid hydrogen are superconductors. Organic crystals, metal oxides, and insulators can have superconductivity.
high temperature
Most high-temperature superconductors are copper oxide {cuprate} layers between other layers. Mercury-barium-calcium copper oxide superconducts at 164 K under 10,000 atm pressure and at 138 K at 1 atm.
Iron and arsenic layers between a lanthanum, cerium, samarium, neodymium, or praseodymium layer and an oxygen or fluoride layer can superconduct up to 52 K. Magnesium boride superconducts at 39 K. Bismuth, strontium, calcium, copper, and oxygen atoms can combine to make BSCCO high-temperature superconductor. Yttrium, barium, copper, and oxygen atoms can combine to make YBCO high-temperature superconductor.
cause
Large-scale quantum effects cause superconductivity, which happens when energies are small, such as at low temperature. Bosons in same quantum state can condense {Bose-Einstein condensation, superconductivity} (BEC) from gas to liquid. Repulsive bosons condense better. Materials can Bose-Einstein-condense at cold temperatures.
Fermions, such as electrons, form Cooper pairs at temperature lower than temperature at which material becomes degenerate Fermi gas. Both electrons have same spin. Making electron pairs makes positive metal ions. Cooper pairs have streamline flow through metal ions and travel with no resistance.
Fermions can pair more easily if attraction increases. Electrons can resonate {Feshbach resonance} in magnetic fields {magnetic resonance} and so pair better.
Magnetic flux has quanta in superconductors. Electric field has no quanta but quantizing it can make calculations easier.
magnetic field
Outside magnetic field can enter only short distance into superconductors with current, because photons acquire mass as electromagnetic gauge symmetry breaks spontaneously.
insulator
Forcing atoms {Mott insulator} in Bose-Einstein condensates to have definite positions changes quantum properties.
In superconducting materials, electrons distort positive-ion lattice to make phonons, which interact with other electrons, causing attraction and electron pairing {BCS theory}. Critical temperature is higher if more electrons can go to superconductive state, if lattice-vibration frequencies are higher, and if electrons and lattice interact stronger. Mercury-barium-calcium copper oxide does not follow BCS theory. Magnesium boride follows BCS theory. Liquid oxygen, liquid nitrogen, and liquid hydrogen follow BCS theory.
Fermions can pair {Cooper pair} at temperatures much lower than temperature at which system is degenerate Fermi gas.
Systems {degenerate Fermi gas} can have one fermion in each low-energy quantum state.
Devices {transition edge sensor} can detect photons at transition temperature to superconductivity.
5-Physics-Electromagnetism-Conductivity
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Date Modified: 2022.0225