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We report systematic 57 Fe-NMR and 75 As-NMR/NQR studies on an underdoped sample (T c ¼ 20 K), an optimally doped sample (T c ¼ 28 K), and an overdoped sample (T c ¼ 22 K) of oxygen-deficient iron (Fe)-based oxypnictide superconductor LaFeAsO 1Ày . A microscopic phase separation between superconducting domains and magnetic domains is shown to take place in the underdoped sample, indicating a local inhomogeneity in association with the density distribution of oxygen deficiencies. As a result, 1=T 1 T in the normal state of the superconducting domain decreases significantly upon cooling at both the Fe and As sites regardless of the electron-doping level in LaFeAsO 1Ày . On the basis of this result, we claim that 1=T 1 T is not always enhanced by antiferromagnetic fluctuations close to an antiferromagnetic phase in the underdoped superconducting sample. This contrasts with the behavior in hole-doped Ba 0:6 K 0:4 Fe 2 As 2 (T c ¼ 38 K), which exhibits a significant increase in 1=T 1 T upon cooling. We remark that the crucial difference between the normal-state properties of LaFeAsO 1Ày and Ba 0:6 K 0:4 Fe 2 As 2 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.

Superconductivity without spatial inversion symmetry has begun to attract much attention since the discovery of the superconductor CePt 3 Si.1 It is presumed that the absence of spatial inversion symmetry causes an admixture between even and odd parities of superconducting pairing due to antisymmetric spin-orbit coupling (ASOC).2 However, there has been no clear evidence of the admixture thus far, and hence the spatial noncentrosymmetric effect on superconductivity remains experimentally controversial. Recently, ASOC has also been discussed in transition-metal superconductors. In this system, we can consider ASOC without strongly correlated electron systems, which would be appropriate for tracing the effect of ASOC. Interestingly, in Li 2 Pt 3 B, it was reported that unconventional superconductivity with a line node and a spin-triplet pairing state emerge, which are ascribed to ASOC.3, 4 These reports suggest that ASOC can induce a novel superconducting state even though there is no strong electron correlation.The intermetallic binary Ir 2 Ga 9 does not possess spatial inversion symmetry and becomes superconducting below T c = 2.2 K.5, 6 Specific heat and resistivity measurements showed that the compound is a weak-coupling BCS superconductor with an isotropic gap, and located near the boundary between type-I and type-II superconductivities with an upper critical field H c2 ∼ 150 Oe. 5, 6In this letter, we report on the characteristics of superconductivity in noncentrosymmetric Ir 2 Ga 9 probed by 71 Ga-nuclear-quadrupole-resonance (NQR) measurement at a zero field (H = 0). The spatial noncentrosymmetric effect on the superconducting state is discussed.A single crystal of Ir 2 Ga 9 was grown by the Ga flux method.6 Powder X-ray diffraction indicated that the compound forms in the primitive monoclinic Rh 2 Ga 9 type structure.6, 7 The sample of Ir 2 Ga 9 was crushed into coarse powder for NQR measurement to allow the penetration of the rf field. The NQR measurement was performed by the conventional spin-echo method in the temperature (T ) range of 1-280 K. T 1 was measured at f ∼ 26.45 MHz, which was the 1ν Q (±1/2 ↔ ±3/2) transition of 71 Ga (I = 3/2), as shown in Fig. 1. The NQR