title: Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe(0.953)Co(0.047))(2)As(2): evidence for a sharp enhancement of spin fluctuations by nematic order.
abstract: Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe(0.953)Co(0.047))(2)As(2). These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at T(S), sets in well above the stripe antiferromagnetic ordering at T(N). We find that the temperature-dependent dynamic susceptibility displays an anomaly at T(S) followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Fernandes
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Jagat
authors.initials: J
authors.lastname: Lamsal
authors.affiliation: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Jiaqiang
authors.initials: J
authors.lastname: Yan
authors.affiliation: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Songxue
authors.initials: S
authors.lastname: Chi
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Tucker
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA.
authors.forename: Daniel K
authors.initials: DK
authors.lastname: Pratt
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Lynn
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Materials Sciences and Engineering, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: McCallum
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Canfield
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Materials Sciences and Engineering, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Lograsso
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: Alan I
authors.initials: AI
authors.lastname: Goldman
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: David
authors.initials: D
authors.lastname: Vaknin
authors.affiliation: Ames Laboratory, Ames, Iowa 50011, USA and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA and Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McQueeney