Periodic DOS modulation in underdoped Bi2223

In this report, we show the results of the STM/STS study on the Bi2223 single crystals whose doping levels were ranging from an optimally doped to an underdoped region. Bi2223 single crystals were grown by a TSFZ method and their doping levels were adjusted with annealing in an oxygen deficient atmosphere. Single crystals were cleaved in an UHV at around 77 K and STM/STS measurements were carried out in the same conditions. We successfully obtained the tunneling spectrum maps as well as topographic images. We found that the superconducting gap was much more homogeneous than in the case of the Bi2212 in optimal doping, but becomes inhomogeneous with decreasing a doping level. This suggests the decoupling of the three Cu-O layers in terms of the SC correlation. More importantly, we found a new periodic modulation in the LDOS map with periods about 2a0, which was almost dispersion-less and observed only in the underdoped TC=85 K sample. This modulation is possibly related to the charge/spin order in the inner plane, which is supposed to be highly undrerdoped.Comment: 4pages, 3 Figures. PD

Stripe antiferromagnetic correlations in LaFeAsO1-xFx probed by 75As NMR

The anisotropy of the nuclear spin-lattice relaxation rate $1/T_{1}$ of $^{75}$As was investigated in the iron-based superconductor LaFeAs(O$_{1-x}$F$_{x}$) ($x = 0.07, 0.11$ and 0.14) as well as LaFeAsO. While the temperature dependence of the normal-state $1/T_1T$ in the superconducting (SC) $x = 0.07$ is different from that in the SC $x = 0.11$, their anisotropy of $1/T_1$, $R \equiv (1/T_{1})_{H \parallel ab}/(1/T_{1})_{H \parallel c}$ in the normal state is almost the same ($\simeq$ 1.5). The observed anisotropy is ascribable to the presence of the local stripe correlations with $Q = (\pi, 0)$ or $(0, \pi)$. In contrast, $1/T_1$ is isotropic and $R$ is approximately 1 in the overdoped $x = 0.14$ sample, where superconductivity is almost suppressed. These results suggest that the presence of the local stripe correlations originating from the nesting between hole and electron Fermi surfaces is linked to high-$T_c$ superconductivity in iron pnictides.Comment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.

^{31}P and ^{75}As NMR evidence for a residual density of states at zero energy in superconducting BaFe_2(As_{0.67}P_{0.33})_2

^{31}P and ^{75}As NMR measurements were performed in superconducting BaFe_2(As_{0.67}P_{0.33})_2 with T_c = 30 K. The nuclear-spin-lattice relaxation rate T_1^{-1} and the Knight shift in the normal state indicate the development of antiferromagnetic fluctuations, and T_1^{-1} in the superconducting (SC) state decreases without a coherence peak just below T_c, as observed in (Ba_{1-x}K_{x})Fe_2As_2. In contrast to other iron arsenide superconductors, the T_1^{-1} \propto T behavior is observed below 4K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe_2(As_{1-x}P_{x})_2 despite a comparable T_c value, an analogous phase diagram, and similar Fermi surfaces to (Ba_{1-x}K_{x})Fe_2As_2.Comment: 4 pages, 5 figure

Near-Infrared search for C IV absorption counterparts along the line-of-sights to pair quasars

We carried out a Subaru and UKIRT near infrared imaging survey for H-alpha emitting galaxies around two pair quasar systems (Q0301-005/Q0302-003 and Q2343+125/Q2344+125), and a triple quasar system (KP76/KP77/KP78). Narrow band near infrared filters covering the H-alpha emission expected for galaxies at the confirmed C IV absorption redshift toward the quasar systems were used for this survey. These quasar pairs or triplet are separated at most by 17 arcmins (~5 h^-1 Mpc in proper distance) from each other on the sky, and have common C IV absorption lines at almost identical redshifts at z=2.24-2.43, which suggests there could be a Mpc-scale absorbing systems such as a cluster, or a group, of galaxies that cover all the line-of-sights to the pair/triple quasars. Using narrow-band deep images, we detected five candidates for H-alpha emitting galaxies around two of the six fields, Q2343+125 and Q2344+125, whose apparent star formation rates are, extremely high, 20-466 M_solar/year. However, all or most of them are not likely to be galaxies at the absorption redshift but galaxies at lower redshift, because of their extreme brightness. In the fields of the other quasars, we detected no star-forming galaxies, nor did we find any number excess of galaxy counts around them. This no-detection results could be because the luminosities and star formation rates of galaxies are lower than the detection limits of our observations (K' > 21 and SFR < 1.8-240 h^-2 M_solar/year). They could be located outside of the observed fields by chance. Otherwise, most C IV absorption lines could be ascribed not to cluster of galaxies, but to isolated star forming pockets far from bright galaxies and could be analogous objects to weak Mg II absorbers.Comment: 9 pages, including 5 figures; accepted for publication in the Astronomical Journa

鉄系超伝導体BaFe2(As[1-x]Px)2の核磁気共鳴による研究

京都大学0048新制・課程博士博士(理学)甲第18051号理博第3929号新制||理||1567(附属図書館)30909京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 石田 憲二, 教授 前野 悦輝, 教授 松田 祐司学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA

Gradual suppression of antiferromagnetism in BaFe_{2}(As_{1−x}P_{x})_{2}: Zero-temperature evidence for a quantum critical point

Static and dynamic magnetic properties of lightly P-substituted BaFe_{2}(As_{1−x}P_{x})_{2} were systematically investigated by ^{31}P NMR. The averaged internal magnetic field at the P site in the zero-temperature limit evaluated from the broadening of NMR spectra in the antiferromagnetic (AFM) phase is gradually suppressed toward x∼0.35 with increasing x, which provides definitive evidence for the existence of an AFM quantum critical point (QCP) at x∼0.35. The location of the AFM QCP is consistent with the previous estimation from temperature dependence of spin dynamics in the normal state, and the superconducting transition temperature Tc takes the maximum around the QCP. Our experiments, revealing a signature of a QCP extending up to room temperature, establish BaFe_{2}(As_{1−x}P_{x})_{2} as one of the most accessible systems for unraveling the nature of quantum criticality and the relationship between AFM quantum criticality and unconventional superconductivity