Put differently, for the fact that spin is relevant in Fe pnictide superconductors, they are basically itinerant magnetism suggesting that the Mott - Hubbard physics may be irrelevant in physics of Fe pnictide superconductors.
We speculate that the normal Landau theory developed for 2nd order phase transition may not adequately account for the physics of the phase transitions and associated phenomena, for example, magneto-volume effect due to lattice anharmonicity in Fe pnictide superconductors.
Common high-temperature superconducting materials include bismuth strontium calcium copper oxide (BSCCO), lanthium barium copper oxide, yttrium barium copper oxide (YBCO), iron pnictides
, and mercury barium calcium copper oxide.
Our finding of a quantum critical point in iron pnictides
opens the door for new avenues of research into this important class of materials," said University of Tennessee/ORNL physicist Pengcheng Dai, a neutron scattering specialist.