Doping dependence of Normal-state Property in the Iron-based Oxypnictide Superconductors LaFeAsO1-y probed by 57Fe-NMR and 75As-NMR/NQR

H. Mukuda; N. Terasaki; N. Tamura; H. Kinouchi; M. Yashima; Y. Kitaoka; K. Miyazawa; P. M. Shirage; S. Suzuki; S. Miyasaka; S. Tajima; H. Kito; H. Eisaki; A. Iyo

doi:10.1143/JPSJ.78.084717

paper

Doping dependence of Normal-state Property in the Iron-based Oxypnictide Superconductors LaFeAsO1-y probed by 57Fe-NMR and 75As-NMR/NQR

arXiv:0904.4301 · doi:10.1143/JPSJ.78.084717

Abstract

We report systematic 57Fe-NMR and 75As-NMR/NQR studies on an underdoped sample (T_c=20 K), an optimally doped sample (T_c=28 K), and an overdoped sample (T_c=22 K) of oxygen-deficient iron (Fe)-based oxypnictide superconductor LaFeAsO_{1-y} $. A mi cr osco p i c p ha sese p a r a t i o nb e tw ee n s u p er co n d u c t in g d o main s an d ma g n e t i c d o main s i ss h o w n t o t ak e pl a ce in t h e u n d er d o p e d s am pl e, in d i c a t in g a l oc a l inh o m o g e n e i t y ina ssoc ia t i o n w i t h t h e d e n s i t y d i s t r ib u t i o n o f o x y g e n d e f i c i e n c i es . A s a r es u l t, 1/ T_{1} T in t h e n or ma l s t a t eo f t h es u p er co n d u c t in g d o main d ecr e a sess i g ni f i c an tl y u p o n coo l in g a t b o t h t h e F e an d A ss i t esr e g a r d l esso f t h ee l ec t r o n - d o p in g l e v e l in L a F e A s O_{1 - y} . O n t h e ba s i so f t hi sr es u l t, w ec l aim t ha t$ 1/T_1T $i s n o t a l w a y se nhan ce d b y an t i f er r o ma g n e t i c f l u c t u a t i o n sc l ose t o anan t i f er r o ma g n e t i c p ha se in t h e u n d er d o p e d s u p er co n d u c t in g s am pl e . T hi sco n t r a s t s w i t h t h e b e ha v i or inh o l e - d o p e d B a_{0.6} K_{0.4} F e 2 A s 2 (T_{c} = 38 K), w hi c h e x hibi t s a s i g ni f i c an t in cr e a se in$ 1/T_1T$ upon cooling. We remark that the crucial difference between the normal-state properties of LaFeAsO_{1-y} and Ba_{0.6}K_{0.4}Fe2As2 originates from the fact that the relevant Fermi surface topologies are differently modified depending on whether electrons or holes are doped into the FeAs layers.

8 pages, 13 figures, to be published in J. Phys. Soc. Jpn. Vol. 78 No. 8