Nanoscopic coexistence of magnetic and superconducting states within the FeAs layers of ${\text{CeFeAsO}}_{1-x}{\text{F}}_x$

We report on the coexistence of magnetic and superconducting states in ${\text{CeFeAsO}}_{1-x}{\text{F}}_x$ for $x=0.06\left(2\right)$, characterized by transition temperatures $T_m=30\text{K}$ and $T_c=18\text{K}$, respectively. Zero-field and transverse-field muon-spin-relaxation measurements show that below 10 K the two phases coexist within a nanoscopic scale over a large volume fraction. This result clarifies the nature of the magnetic-to-superconducting transition in the ${\text{CeFeAsO}}_{1-x}{\text{F}}_x$ phase diagram, by ruling out the presence of a quantum critical point which was suggested by earlier studies.

Figure 1

(Color online) Magnetic susceptibility in zero-field cooling of ${\text{CeFeAsO}}_{1-x}{\text{F}}_x$ with $x=0.06\left(2\right)$, plotted in SI units. The solid curve represents a phenomenological fit to the susceptibility for temperatures above the ordering of Ce magnetic sublattice $T_N^{\text{Ce}}$. The superconducting (dashed line) and the Curie-Weiss (dotted line) contributions are also displayed (see text for details).

Figure 2

(Color online) Time dependence of the normalized zero-field muon asymmetry with best fits to Eq. (1), measured at four different temperatures.

Figure 3

(Color online) (a) Temperature dependence of the magnetic (triangles) and nonsuperconducting (solid line) volume fractions as seen by ZF-$\mu \text{SR}$ and magnetization measurements, respectively. The onset of superconducting and magnetic transitions, $T_c$ and $T_m$, is indicated by vertical arrows. (b)–(d) panels display the fraction, the decay rate, and the relative field shift for the $j=1$ fraction of the TF-$\mu \text{SR}$ asymmetry [Eq. (2)].