Emergence of Novel Antiferromagnetic Order Intervening between Two Superconducting Phases in LaFe(As_1-x_P_x_)O: 31P-NMR Studies

TL;DR

This study uses 31P-NMR to map the phase diagram of LaFe(As_{1-x}P_{x})O, revealing a novel antiferromagnetic phase between two superconducting phases and highlighting the role of orbital-specific fluctuations in superconductivity.

Contribution

It uncovers a new antiferromagnetic phase (AFM-2) in LaFe(As_{1-x}P_{x})O and links orbital-specific spin fluctuations to superconductivity.

Findings

Discovery of AFM-2 phase between two SC phases.

Identification of orbital-specific density of states at the Fermi level.

Correlation between spin fluctuations and superconductivity.

Abstract

We revealed novel phase deagram of Fe-pnictide high-Tc superconductor LaFe(As_{1-x}P_{x})O in wide doping level (0.3<x<1) by P-NMR. Systematic 31P-NMR studies revealed the emergence of the antiferromagnetic ordered phase (AFM-2) in 0.4 < x < 0.7 that intervenes between two superconductivity (SC-1/SC-2) phases. The 31P-NMR Knight shift points to the appearance of the sharp density of states at the Fermi level that is derived from d_{3Z^2?r^2} orbit, which is less relevant with the onset of the SC-2. On the other hand, we remark that the AFM spin fluctuations arising from the interband nesting on the d_{XZ}/d_{YZ} orbits must be a key ingredient for the occurrence of SC around AFM-2.