Resistivity anisotropy of AFe(2)As(2) (A=Ca, Sr, Ba): Direct versus Montgomery technique measurements

TitleResistivity anisotropy of AFe(2)As(2) (A=Ca, Sr, Ba): Direct versus Montgomery technique measurements
Publication TypeJournal Article
Year of Publication2009
AuthorsTanatar MA, Ni N, Samolyuk GD, Bud'ko SL, Canfield PC, Prozorov R
Journal TitlePhysical Review B
Date Published04/01
ISBN Number1098-0121
Accession NumberISI:000265942800128
Keywordsbarium compounds, calcium compounds, electrical resistivity, electronic structure, fermi surface, fermi-surface, high-temperature superconductors, iron compounds, magnetic transition temperature, strontium compounds, superconductivity

The anisotropy of electrical resistivity was measured in parent compounds of the iron-arsenic high-temperature superconductors AFe(2)As(2) with alkali earth elements A=Ca, 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 gamma(rho)=rho(c)/rho(a) 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 T-SM, with the change mainly coming from stronger variation in rho(a) as compared with rho(c). 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 A ion. Our results show that the electronic structure of the iron pnictides has large contribution from three-dimensional areas of the Fermi surface.

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