NMR Studies on the Superconducting Symmetry of Iron Pnictide Systems

TL;DR

This study uses NMR techniques to investigate the superconducting symmetry in iron pnictide systems, revealing unusual relaxation behaviors and absence of coherence peaks, challenging existing theories.

Contribution

It provides new NMR data on LaFe1-yCoyAsO1-xFx samples, highlighting atypical relaxation rates and discussing implications for superconducting symmetry.

Findings

Superconducting samples show relaxation rates different from previous reports.

No coherence peak observed in the relaxation data.

Results challenge existing theories on superconducting symmetry.

Abstract

NMR longitudinal relaxation rates 1/T1 and Knight shifts K have been measured for superconducting samples of LaFe1-yCoyAsO1-xFx with y=0.0 and 0.0075 and for a nonsuperconducting metallic sample with y=0.1, where the x values are always fixed at 0.11. The temperature (T) dependence the relaxation rates 1/T1 of the superconducting samples has been found to be markedly different from the behavior 1/T1 T^(2.5-3.0) reported by many groups in the entire T range measured (from the temperature immediately below the superconducting transition temperature Tc down to (0.1-0.2)Tc). The nonexistence of the coherence peak has also been found. Based on the results of the measurements and other kinds of existing data, arguments are presented on the superconducting symmetry of the Fe pnictide systems, where the several points which cannot be easily understood by existing theories, are pointed out. Results of the measurements on the nonsuperconducting metallic samples are also presented.