Quantum critical behavior in heavily doped LaFeAsO${}_{1-x}$H${}_x$ pnictide superconductors analyzed using nuclear magnetic resonance

Abstract

We studied the quantum critical behavior of the second antiferromagnetic (AF) phase in the heavily electron-doped high-$T_c$ pnictide, LaFeAsO${}_{1-x}$H${}_x$ by using ${}^{75}$As and ${}^1$H nuclear-magnetic-resonance (NMR) technique. In the second AF phase, we observed a spatially modulated spin-density-wave-like state up to $x$=0.6 from the NMR spectral lineshape and detected a low-energy excitation gap from the nuclear relaxation time $T_1$ of ${}^{75}$As. The excitation gap closes at the AF quantum critical point (QCP) at $x\approx 0.49$. The superconducting (SC) phase in a lower-doping regime contacts the second AF phase only at the AF QCP, and both phases are segregated from each other. The absence of AF critical fluctuations and the enhancement of the in-plane electric anisotropy are key factors for the development of superconductivity.

arXiv commentaccepted in Phys. Rev. B

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• Quantum Phase transition under pressure in a heavily hydrogen-doped iron-based superconductor LaFeAsO
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• Magnetism driven by strong electronic correlation in the heavily carrier-doped iron oxypnictide LaFeAsO${}_{0.49}$H${}_{0.51}$
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• Universal quasi-degenerate orbital origin of two-dome phases in iron pnictide superconductors
• Crystalline anisotropy induces a second antiferromagnetic phase in the absence of SDW in the heavily hydrogen-doped LaFeAsO${}_{1-x}$H${}_x$ $(x\sim 0.5)$