Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Nat Commun. 2013;4:2265. doi: 10.1038/ncomms3265.
A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe(2-x)Ni(x)As₂ (0≤x≤0.17). We find two critical points at x(c1)=0.10 and x(c2)=0.14. The electrical resistivity follows ρ=ρ₀+AT(n), with n=1 around x(c1) and another minimal n=1.1 at x(c2). By NMR measurements, we identity x(c1) to be a magnetic quantum critical point and suggest that x(c2) is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.
量子临界点是系统相图中的一个点，在该点处，在绝对零度温度 (T) 下完全抑制了有序。量子临界点的存在表现在有限 T 的物理性质中，并且常常导致物质的新状态。许多人认为，铜酸盐和重费米子材料中的超导性是由与量子临界点相关的涨落介导的。在最近发现的铁磷化物超导体中，我们报告了 BaFe(2-x)Ni(x)As₂ (0≤x≤0.17) 的输运和 NMR 测量结果。我们发现两个临界点，x(c1)=0.10 和 x(c2)=0.14。电阻率遵循 ρ=ρ₀+AT(n)，其中 n=1 左右在 x(c1)，而在 x(c2)处的另一个最小值为 n=1.1。通过 NMR 测量，我们确定 x(c1)为磁量子临界点，并建议 x(c2)是与向列结构相变相关的新型量子临界点。我们的结果表明，载流子掺杂磷化物中的超导性与量子临界点密切相关。
