Fe1+δSexTe1-xにおける超伝導と反強磁性量子臨界点近傍の物性

概要

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Macroscopic and microscopic physical properties of Fe1+δSexTe1-x were investigated through the magnetic susceptibility, electrical resistivity, heat capacity and nuclear magnetic resonance (NMR) measurements. The mother compound Fe1.14Te shows an antiferromagnetic phase transition accompanied by the structural change at 61.5K. The antiferromagnetic transition temperature of Fe1+δSexTe1-x decreases with increasing x, then the superconducting transition appears above x = 0.2. The superconductivity with clean limit occurs when δ is small. In such a compound, the temperature dependence of the nuclear spin - lattice relaxation rate and the electron contributed specific heat reveals presence of the nodal superconducting gap structure, suggesting that the superconductivity occurs in an unconventional mechanism. From a systematic investigation of the nuclear spin - lattice relaxation rate in Fe1+δSexTe1-x, it was found that the antiferromagnetic quantum critical point lies at x ∼0.03. The superconductivity occurs in the vicinity of the antiferromagnetic quantum critical point, resulting in that the superconductivity in Fe1+δSexTe1-x is mediated by the antiferromagnetic spin fluctuations.