<研究ノート>鉄カルコゲナイド超伝導体における反強磁性揺らぎ

Abstract

Macroscopic and microscopic physical properties of Fe1+δTe1-xSex were investigated from magnetic susceptibility, electrical resistivity, heat capacity and nuclear magnetic resonance (NMR) measurements. The mother compound Fe1.14Te shows an antiferromagnetic phase transition accompanied by structural change at 61.5 K. The magnetic transition temperature in Fe1+δTe1-xSex decreases with increasing x, then a bulk superconductivity appears below x = 0.3. The superconductivity with clean limit occurs when δ is small. In such compounds, the temperature dependence of the nuclear spin–lattice relaxation rate and the electron contributed specific heat reveal the presence of the nodal superconducting gap structure, indicating that the superconductivity is an unconventional one. From the systematic investigations in Fe1+δTe1-xSex, the nuclear spin–lattice relaxation rate reveals that the antiferromagnetic quantum critical point lies at x ~ 0.03. The superconductivity occurs in the vicinity of the antiferromagnetic quantum critical point, suggesting that the superconductivity of Fe1+δTe1-xSex is attributed to the antiferromagnetic spin fluctuations.