Researchers have discovered an unusual temperature behavior of the electrons in iron arsenic superconductors that may play a crucial role in the emergence of high temperature superconductivity. The electrons in solids occupy areas called pockets. In regular metals the sizes of these pockets remain constant as a function of temperature and are proportional to number of electrons that conduct current. Surprisingly, in iron arsenic high temperature superconductors, the pocket associated with empty electron states, known as holes, decreases and ones associated with electrons expand, as if there were more conduction electrons. More importantly, at low temperatures, the hole and electron pockets are about the same size and shape. This is a condition called "nesting", which often leads to special magnetic state called "antiferromagnetic order" in which the magnetic moments of adjacent ions point in opposite directions. This state is believed to be a key to the emergence of high temperature superconductivity in iron arsenic superconductors. Knowledge of how the temperature affects nesting and the destruction of antiferromagnetic order may be key to enhancing the critical superconducting temperature and searching for new superconducting materials.
R. S. Dhaka, S. E. Hahn, E. Razzoli, Rui Jiang, M. Shi, B. N. Harmon, A. Thaler, S. L. Bud'ko, P. C. Canfield and Adam Kaminski "Unusual Temperature Dependence of Band Dispersion in Ba(Fe1-xRux)2As2 and its Consequences for Antiferromagnetic Ordering" Physical Review Letters, 2013, 110, 067002.