Uniaxial-strain mechanical detwinning of CaFe2As2 and BaFe2As2 crystals: Optical and transport study

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Tanatar, M.A.
Blomberg, E.C.
Kreyssig, A.
Kim, M.G.
Ni, N.
Thaler, A.
Bud'ko, S.L.
Mazin, I.I.
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American Physical Society
Canfield, Paul
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Goldman, Alan
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Physics and Astronomy
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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The parent compounds of iron-arsenide superconductors, AFe(2)As(2) (A = Ca, Sr, Ba), undergo a tetragonal to orthorhombic structural transition at a temperature T-TO in the range 135-205 K depending on the alkaline-earth element. Below T-TO the free standing crystals split into equally populated structural domains, which mask intrinsic, in-plane, anisotropic properties of the materials. Here we demonstrate a way of mechanically detwinning CaFe2As2 and BaFe2As2. The detwinning is nearly complete, as demonstrated by polarized light imaging and synchrotron x-ray measurements, and reversible, with twin pattern restored after strain release. Electrical resistivity measurements in the twinned and detwinned states show that resistivity, rho, decreases along the orthorhombic a(o) axis but increases along the orthorhombic b(o) axis in both compounds. Immediately below T-TO the ratio rho(bo)/rho(ao) = 1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to CaFe2As2, BaFe2As2 reveals an anisotropy in the nominally tetragonal phase, suggesting that either fluctuations play a larger role above T-TO in BaFe2As2 than in CaFe2As2 or that there is a higher temperature crossover or phase transition.
This article is published as Tanatar, M. A., E. C. Blomberg, A. Kreyssig, M. G. Kim, N. Ni, A. Thaler, S. L. Bud’Ko et al. "Uniaxial-strain mechanical detwinning of CaFe 2 As 2 and BaFe 2 As 2 crystals: Optical and transport study." Physical Review B 81, no. 18 (2010): 184508. DOI: 10.1103/PhysRevB.81.184508. Copyright 2010 American Physical Society. Posted with permission.