Gradual suppression of antiferromagnetism in BaFe_{2}(As_{1−x}P_{x})_{2}: Zero-temperature evidence for a quantum critical point

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Static and dynamic magnetic properties of lightly P-substituted BaFe_{2}(As_{1−x}P_{x})_{2} were systematically investigated by ^{31}P NMR. The averaged internal magnetic field at the P site in the zero-temperature limit evaluated from the broadening of NMR spectra in the antiferromagnetic (AFM) phase is gradually suppressed toward x∼0.35 with increasing x, which provides definitive evidence for the existence of an AFM quantum critical point (QCP) at x∼0.35. The location of the AFM QCP is consistent with the previous estimation from temperature dependence of spin dynamics in the normal state, and the superconducting transition temperature Tc takes the maximum around the QCP. Our experiments, revealing a signature of a QCP extending up to room temperature, establish BaFe_{2}(As_{1−x}P_{x})_{2} as one of the most accessible systems for unraveling the nature of quantum criticality and the relationship between AFM quantum criticality and unconventional superconductivity.