title: Unconventional London penetration depth in single-crystal Ba(Fe0.93Co0.07)2As2 superconductors.
abstract: The London penetration depth lambda(T) has been measured in single crystals of Ba(Fe0.93Co0.07)2As2. The observed low-temperature variation of lambda(T) follows a power law, Deltalambda(T) approximately T(n) with n approximately 2.4+/-0.1, indicating the existence of normal quasiparticles down to at least 0.02T(c). This is in contrast with previous penetration depth measurements on single crystals of NdFeAsO1-xFx and SmFeAsO1-xFx, which indicate an anisotropic but nodeless gap. We discuss possible explanations of the observed power law behavior.
authors.affiliation: Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
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authors.initials: RT
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authors.lastname: Ni
authors.forename: C
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authors.lastname: Samolyuk
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authors.lastname: Schmalian
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authors.lastname: Nandi
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authors.lastname: Kreyssig
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authors.lastname: Goldman
authors.forename: J Q
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authors.lastname: Bud'ko
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authors.initials: PC
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authors.lastname: Prozorov