Spin density wave and superconductivity in CaFe₁₋xCoxAsF studied by nuclear magnetic resonance

Abstract

We performed nuclear magnetic resonance measurements to investigate the evolution of spin-density-wave (SDW) and superconducting (SC) states upon electron doping in CaFe₁₋x AsF, which exhibits an intermediate phase diagram between those of LaFeAsO₁₋x and Ba(Fe₁₋xCox)₂. We found that homogeneous coexistence of the incommensurate SDW and SC states occurs only in a narrow doping region around the crossover regime, which supports S₊₋ -wave symmetry. However, only the structural phase transition survives upon further doping, which agrees with predictions from orbital fluctuation theory. The transitional features upon electron doping imply that both spin and orbital fluctuations are involved in the superconducting mechanism.