Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study

TL;DR

This NMR study investigates the coupling between 4f and itinerant electrons in SmFeAsO$_{1-x}$F$_x$ superconductors, revealing behavior similar to heavy-fermion systems and showing no change in relaxation rate across the superconducting transition.

Contribution

It provides new insights into electron coupling in SmFeAsO$_{1-x}$F$_x$ superconductors using $^{19}$F NMR, highlighting similarities with heavy-fermion compounds and challenging single-band models.

Findings

Relaxation rate $1/T_1$ increases upon cooling.

Behavior matches self-consistent renormalization theory.

No change in $1/T_1$ across superconducting transition.

Abstract

$^{19}$F NMR measurements in SmFeAsO$_{1-x}$F$_x$, for $0.15\leq x\leq 0.2$, are presented. The nuclear spin-lattice relaxation rate $1/T_1$ increases upon cooling with a trend analogous to the one already observed in CeCu$_{5.2}$Au$_{0.8}$, a quasi two-dimensional heavy-fermion intermetallic compound with an antiferromagnetic ground-state. In particular, the behaviour of the relaxation rate either in SmFeAsO$_{1-x}$F$_x$ or in CeCu$_{5.2}$Au$_{0.8}$ can be described in the framework of the self-consistent renormalization theory for weakly itinerant electron systems. Remarkably, no effect of the superconducting transition on $^{19}$F $1/T_1$ is detected, a phenomenon which can hardly be explained within a single band model.