We report the 75 As nuclear quadrupole resonance (NQR) and specific heat measurements of the heavily hole-doped superconductor KFe 2 As 2 (superconducting transition temperature T c ' 3:5 K). The spin-lattice relaxation rate 1=T 1 in the superconducting state exhibits a gradual temperature dependence with no coherence peak below T c . The quasiparticle specific heat C QP =T shows a small jump, which is about 30% of the electronic specific heat coefficient just below T c . The C QP =T suggests the existence of low-energy quasiparticle excitation at the lowest measurement temperature T ¼ 0:4 K ' T c =10. The T dependences of 1=T 1 and C QP =T can be explained by a multiple nodal superconducting gap scenario rather than by a multiple fully gapped s AE -wave scenario determined using simple gap analysis.

We report the 75 As nuclear magnetic resonance (NMR) measurement of the hole-doped superconductor Ba 1Àx K x Fe 2 As 2 with different lattice parameters and different superconducting volume fractions (T c ' 38 K).75 As-NMR spectra revealed that the magnetically ordered and superconducting phases are microscopically separated. The spin-lattice relaxation rate 1=T 1 in the normal state reflects the existence of a large two-dimensional antiferromagnetic spin fluctuation. The 1=T 1 in the superconducting state down to the lowest measurement temperature T varies close to T 3 . In addition, it exhibits no coherence peak just below T c . This shows a T dependence similar to those of other iron pnictides.KEYWORDS: Ba 1Àx K x Fe 2 As 2 , superconductivity, magnetic order, phase separation, nuclear magnetic resonance DOI: 10.1143/JPSJ.78.033704The discovery of superconductivity in F-doped LaFeAsO with a superconducting transition temperature T c ¼ 26has accelerated further investigations of related superconductors.2-9) The 3d electrons originating from an FeAs layer form multiple bands at the Fermi level and play an important role in superconductivity. 10,11) In particular, nondoped materials commonly exhibit an antiferromagnetic (AF) order with an adjacent structural phase transition, which resembles the parent materials of high-T c cuprates. Hence, the relation between magnetic order and superconductivity is one of the vital issues in the investigations of such compounds. K-doped BaFe 2 As 2 is the firstly reported oxygen-free iron-pnictide superconductor with T c ¼ 38 K.6) The crystal structure of Ba 1Àx K x Fe 2 As 2 is of the ThCr 2 Si 2 -type. This structure possesses an FeAs layer similar to that realized in LaFeAsO. The parent material BaFe 2 As 2 exhibits AF anomaly at T N ¼ 140 K.12) Neutron diffraction measurements revealed an ordered moment of 0.87 B (Bohr magneton) at the Fe site with a q vector of ð1; 0; 1Þ for the orthorhombic structure.13) It is important to note that this compound exhibits structural phase transition as well as AF anomaly.12,13) The zero-field 75 As-NMR spectrum also revealed that the magnetically ordered state of this compound is commensurate.14,15) The evaluated H int at 4.2 K decreases gradually with increasing pressure.16) The results are consistent with the other group's NMR results obtained using single crystals. 17)Several groups reported the phase diagram of Ba 1Àx K xFe 2 As 2 . 18,19) For the compound, the AF anomaly disappears and superconductivity is induced by hole doping, K substitution for Ba. The superconducting (SC) state is confirmed to be the bulk from the specific heat jump at T c . 20)The most striking feature of the phase diagram is that the SC region widely spreads for 0:2 x 1 and thus the possibility of the coexistence of the AF and SC states exists for 0:2 x 0:4. Bulk measurements cannot determine whether or not this coexistence is macroscopic. Hence, measurements with a local probe are strongly required. Recent SR measurements show the existence of the phase-sepa...

1)has accelerated further investigations of the related superconductors. [2][3][4] The common feature of these compounds is the possession of an FeAs layer, which is analogous to the CuO 2 plane in high-superconducting-transition-temperature (high-T c ) cuprates. Soon after the intensive investigations of the oxypnictides, the oxygen-free iron pnictide BaFe 2 As 2 5)was proposed as the next-candidate parent material of superconductors with high T c . The crystal structure of this pnictide is the ThCr 2 Si 2 -type structure and possesses a similar FeAs layer to that realized in LaFeAsO. Moreover, this material exhibits spin density wave (SDW) anomaly at T SDW ¼ 140 K (BaFe 2 As 2 ). 5,6) It is important to note that the compound exhibits structural phase transition from tetragonal (I4=mmm) to orthorhombic (Fmmm) as well as SDW anomaly. 5,6) The most striking feature of this compound is that the SDW anomaly disappears and superconductivity is induced by hole doping, for example, K substitution for Ba. 7) In addition, the pressure P-induced superconductivity in BaFe 2 As 2 has recently been reported by the magnetic susceptibility measurements at pressures of up to about 6 GPa. 8) Although it should be revealed by additional experimental approaches whether this superconductivity is intrinsic, it is clear that the investigation of this compound under pressure is important. To understand the relationship between the SDW instability and expected superconductivity in BaFe 2 As 2 , we performed resistivity and zero-externalfield (ZF)75 As nuclear-magnetic-resonance (NMR) measurements of BaFe 2 As 2 under high pressure.In our previous letter, we reported the 75 As-NMR spectra of BaFe 2 As 2 at various temperatures and the temperature T dependence of the spin-lattice relaxation rate 1=T 1 of 75 As under ambient pressure.9) 75 As-NMR spectra clearly revealed that magnetic transition occurs at around 131 K in our samples, which corresponds to the emergence of spin density wave. The T dependence of the internal magnetic field H int suggested that the transition is likely of the first order. We also deduced from the difference in linewidth between the highly and partially oriented powders that the H int at the As site is parallel to the c-axis. The steep decrease in 1=T 1 below T SDW was observed to be due to the gap formation of the SDW at a certain part of the Fermi surface. 1=T 1 below approximately 100 K was nearly proportional to T, which indicates the relaxation due to the remaining conduction electron at the Fermi level even below T SDW . In our previous paper, we also reported a ZF 75 As-NMR spectrum at 1.5 K.9,10) The ZF 75 As-NMR spectrum clearly revealed that the magnetically ordered state of this compound is commensurate. Furthermore, the center line of the ZF 75 As-NMR spectrum is a good measure of the H int at the As site.Polycrystalline BaFe 2 As 2 samples were synthesized by a high-temperature and high-pressure method. They were confirmed to be nearly single phase by X-ray diffraction analysis. Electrical resis...

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In Drosophila sensory organ development, the balance of activities between proneural genes and repressor genes defines a proneural cluster as a population of competent cells for neural development. In this study, we report the isolation and analysis of the tamou [tain) gene that encodes a cell-cell junction-associated protein, which is homologous to mammalian ZO-1, a member of the membrane-associated guanylate kinase homolog family. The tarn mutation reduces the transcription of a repressor gene, extramacrochaetae, and causes enlargement of a proneural cluster where supernumerary precursor cells emerge, resulting in extra mechanosensory organs in the fly. These results suggest that the membrane-associated Tam protein is involved in the signaling pathway that activates emc expression.[Key Woids: Diosophila-, sensory organ formation; MAGUK protein; emc gene; ZO-1 homolog; signal transduction] Received March 15, 1996; revised version accepted May 30, 1996.The Diosophila peripheral nervous system comprises several types of sensory organs, including external mech anosensory and chemosensory organs, internal tension receptors, and touch receptors. The distribution patterns and position-dependent specifications of these sensory organs are highly reproducible (Ghysen 1980;Vandervorst and Ghysen 1980). The position of a sensory organ in the adult fly depends on the birthplace of its precursor, the sensory organ precursor (SOP) cell, which is singled out from a small group of cells called a proneural cluster in the imaginal disc. It has been shown that Diosophila sensory organ development is programmed genetically, and the framework of the genetic cascade involved has been described (Ghysen and Dambly-Chaudiere 1989;Romani et al. 1989;Cubas et al. 1991;Skeath and Carroll 1991;Campuzano and Modolell 1992;Ghysen et al. 1993). According to the scheme, cells expressing the pro neural genes acquire the potential to initiate neural de velopment, and this proneural gene activity is regulated negatively by the repressor genes. A gain-of-function mutation of the proneural gene or a loss-of-function mu-'These authois contributed equally to this work. ^Present addtess: Fujirebio, Inc., Tokyo 192, Japan. ^Corresponding author. tation of the repressor gene causes expansion of the pro neural cluster and yields extra SOP cells, resulting in supernumerary sensory organs in the fly, whereas a lossof-function mutation of the proneural gene or a gain-offunction mutation of the repressor gene has the opposite effect (Jan and Jan 1990;Ghysen et al. 1993). Thus, a balance between the activities of the proneural and re pressor genes to set up a normal proneural cluster is im portant for ensuring the formation of SOP.All known proneural genes, daughteiless [da], atonal, and achaete [ac], scute [sc], lethal of scute, and asense of the achaete-scute complex, encode basic helix-loop-he lix (bHLH) transcription factors (Villares and Cabrera 1987;Alonso and Cabrera 1988; Gaudy et al. 1988;Cronmiller et al. 1988;Gonzalez et al. 1989;Jarman et al...