Comment on ``Texture in the Superconducting Order Parameter of CeCoIn$_5$ Revealed by Nuclear Magnetic Resonance''

TL;DR

This paper critiques a previous NMR study on CeCoIn$_5$, arguing that its evidence for the FFLO state was due to experimental artifacts rather than a true phase transition.

Contribution

It clarifies that the earlier observed NMR signals suggesting FFLO are caused by excess RF power, not the actual superconducting state.

Findings

The previous NMR evidence for FFLO was due to experimental artifacts.

Proper experimental conditions do not support the existence of FFLO in CeCoIn$_5$.

The true nature of the superconducting state remains consistent with conventional models.

Abstract

The study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been of considerable recent interest. Below the temperature $T^*$ which is believed to be the transition temperature ($T$) to the FFLO phase in CeCoIn$_5$, K. Kakuyanagi et al. (Phys. Rev. Lett. 94, 047602 (2005)) reported a composite NMR spectrum with a tiny component observed at frequencies corresponding to the normal state signal. The results were interpreted as evidence for the emergence of an FFLO state. This result is inconsistent with two other NMR studies of V. F. Mitrovi{\'c} et al. (Phys. Rev. Lett. 97, 117002 (2006)) and B.-L. Young et al. (Phys. Rev. Lett. 98, 036402 (2007)). In this comment we show that the findings of K. Kakuyanagi et al. do not reflect the true nature of the FFLO state but result from excess RF excitation power used in that experiment.