Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Phys Rev Lett. 2013 Jun 21;110(25):257001. doi: 10.1103/PhysRevLett.110.257001. Epub 2013 Jun 18.
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.
我们通过高分辨率同步加速器 X 射线和中子散射研究了电子掺杂 BaFe(2-x)Ni(x)As2 中的结构和磁有序。随着 Ni 掺杂量 x 的增加，BaFe2As2 中近乎同时的四方-正交结构（T(s)）和反铁磁（T(N)）相变逐渐被抑制和分离，导致 T(s)>T(N)，这与之前的观察结果一致。然而，对于 x≥0.065，T(s)和 T(N)之间的温度分离随着 x 的增加而减小，趋向于在最佳超导附近的量子双临界点 x≈0.1。在超导穹顶附近的 x≈0.1 左右，由于在 0.088≲x≲0.104 区域中形成了二次非共格磁相，零温转变被预先阻止，导致 T(N)≈T(c) + 10 K 的有限值，T(c)为超导转变温度。我们的结果表明存在一个避免量子临界点，这预计会强烈影响正常态和超导态的性质。
