Abstract
The anisotropy of electrical resistivity was measured in parent compounds of the iron-arsenic high-temperature superconductors with alkali earth elements , Sr, and Ba. Measurements were performed using both the Montgomery technique and direct resistivity measurements on samples cut along principal crystallographic directions. The anisotropy ratio is well below ten for all compounds in the whole temperature range studied (4–300 K), in notable contrast to previous reports. The anisotropy at room temperature increases from about two in Ca to about four in Sr and Ba. In all compounds the resistivity ratio decreases on cooling through the structural/antiferromagnetic transition temperature , with the change mainly coming from stronger variation in as compared with . This suggests that the transition affects stronger the two-dimensional parts of the Fermi surface. We compare our experimental observations with band-structure calculations, and find similar trend in the evolution of anisotropy with the size of ion. Our results show that the electronic structure of the iron pnictides has large contribution from three-dimensional areas of the Fermi surface.
5 More- Received 4 March 2009
DOI:https://doi.org/10.1103/PhysRevB.79.134528
©2009 American Physical Society