title: Avoided quantum criticality and magnetoelastic coupling in BaFe(2-x)Ni(x)As2.
abstract: We study the structural and magnetic orders in electron-doped BaFe(2-x)Ni(x)As2 by high-resolution synchrotron x-ray and neutron scatterings. Upon Ni doping x, the nearly simultaneous tetragonal-to-orthorhombic structural (T(s)) and antiferromagnetic (T(N)) phase transitions in BaFe2As2 are gradually suppressed and separated, resulting in T(s)>T(N) with increasing x, as was previously observed. However, the temperature separation between T(s) and T(N) decreases with increasing x for x≥0.065, tending toward a quantum bicritical point near optimal superconductivity at x≈0.1. The zero-temperature transition is preempted by the formation of a secondary incommensurate magnetic phase in the region 0.088≲x≲0.104, resulting in a finite value of T(N)≈T(c) + 10  K above the superconducting dome around x≈0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both the normal and superconducting states.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Xingye
authors.initials: X
authors.lastname: Lu
authors.forename: H
authors.initials: H
authors.lastname: Gretarsson
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.forename: Xuerong
authors.initials: X
authors.lastname: Liu
authors.forename: Huiqian
authors.initials: H
authors.lastname: Luo
authors.forename: Wei
authors.initials: W
authors.lastname: Tian
authors.forename: Mark
authors.initials: M
authors.lastname: Laver
authors.forename: Z
authors.initials: Z
authors.lastname: Yamani
authors.forename: Young-June
authors.initials: YJ
authors.lastname: Kim
authors.forename: A H
authors.initials: AH
authors.lastname: Nevidomskyy
authors.forename: Qimiao
authors.initials: Q
authors.lastname: Si
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Dai