走査トンネル顕微鏡および分光から見たビスマス系銅酸化物超伝導体の電子物性

Superconductors are of high interest in many fields besides physics, due to their potential energy saving nature. Hence, they exhibit zero resistance below a critical temperature Tc. Possible applications for superconductors are strong electro magnets, SQUIDs, loss-less electric wires, Quantum Computers (e.g. d-wave), etc. The biggest problem in applying superconductors more widely lies in the still very low Tc. However, increasing Tc strongly requires researching superconducting materials on the energy and nanoscale regime.Currently, the superconductors with the highest Tc under ambient pressure are Mercury (Hg)-based cuprate superconductors, whose Tc is about 150 Kelvin. The Bi-based cuprate superconductors researched at our lab, with a similar crystal structure to the Hg-based cuprates also show a relatively high Tc (～94 K) and are environment-friendly due to the absence of Hg. Bi-based cuprate superconductors have intensively been studied concerning the origin of high Tc superconductivity (SC) and in relation to improving Tc.Impurity effects have the potential to reveal important information about the characteristics of the electronic properties, leading to clarifying the origin of superconductivity. Recently, impurity effects of Iron (Fe), which is substituted for Copper (Cu) inside the Cu-O layer, attract much attention since they cause a large suppression of Tc with an enhancement of the magnetic correlation similar to that of the so-called stripe order. In the present study, I have studied the effects of Fe on superconducting quasiparticles in Bi-based high-Tc cuprates by using Scanning Tunnelling Microscopy and Spectroscopy (STM/S), where the single crystals of which the samples were cut from have been grown using the floating zone method.The STM/S data of the Fe-doped and the Fe-free (pure) Bi-based cuprate superconductors were measured at around 8K. The spatial distribution of the LDOS spectra were measured over a field of view, covering more than ten thousand measurement points with a spatial resolution well below the atomic nearest neighbour distance. The STS spectra were analysed using a self-developed reduction framework. Using the independent algorithms, I have revealed and characterised distortions, produced by the convolution of instrumental and intrinsic perturbations and recovered the atomic, and electronic position information as well as impurity-sites in three dimensional image data. Based on the recovered STM/S data, I evaluated the influence of the quasiparticle lifetime broadening Γ on the energy gap properties such as amplitude, shape and spatial distribution. It was found that the energy gap amplitude Δ and Γ largely depend on the spatial position and the local concentration of Fe, not only on the surface but also in the bulge of the sample. Further, by decoupling Δ from the influence of Γ it was shown that Δ more strongly correlates with the topographic structure of the BiO layer than Γ, which correlates only weakly.超伝導は典型的な省エネルギー材料として知られており、これまで学術面だけでなく応用面からも注目されてきた。超伝導の特徴の一つは、超伝導体が転移温度（Tc）以下でゼロ抵抗を示すことである。この特徴を利用した超伝導体の応用例として、量子コンピュータ、強力な電気磁石、SQUID素子、無損失電線などが知られている。超伝導体を応用する際の最大の問題は、室温と比べTcが非常に低いことである。したがって、より広く超伝導を応用するためにTcを上昇させることが重要であり、そのためには超伝導発現メカニズムの解明、特にナノスケールでのミクロな研究が不可欠である。現在、常圧力下における最高のTcを有する超伝導体として、Tc～150Kの水銀（Hg）系銅酸化物超伝導体が知られている。 この水銀系銅酸化物と類似の結晶構造をもつ銅酸化物としてBi系銅酸化物超伝導体があり、そのTcは比較的高く（Tcmax～94K）、またHgを含まないため環境に優しいことが特徴である。ところで、一般に超伝導に種々の不純物を添加したときの超伝導に対する効果は、超伝導の起源によって質的に異なる。したがって、不純物効果から超伝導発現メカニズムの解明につながるような電子状態に関する情報が得られると期待されている。特に最近、不純物として少量のFeを添加した銅酸化物超伝導体において大きな超伝導抑制効果やストライプ相関の増強が報告され、注目されている。本研究では、原子スケールで準粒子励起スペクトルを調べることができる走査トンネル顕微鏡/トンネル分光装置（STM/S）を用いて、Bi系銅酸化物超伝導体における鉄不純物の添加効果を調べた。測定に用いたBi系銅酸化物単結晶試料（Bi2Sr2CaCu2-xFexO8+δ、以後Bi2212）はフローティングゾーン法により作製した。Bi2212系の鉄添加試料と鉄無添加試料のSTM/Sデータは、共にTcより十分低温のT=8Kで測定された。準粒子励起スペクトル（＝局所状態密度（LDOS））の空間依存性は、最近接原子間隔よりも十分細かい点間隔で測定された。各点で測定された準粒子励起スペクトルをDysonのスペクトル関数によりフィッティングし、超伝導状態におけるエネルギーギャップの大きさΔおよび準粒子寿命Γを求めると、ΔとΓが鉄添加により空間的に不均一になることがわかった。その不均一さは試料表面および試料内部における局所的な鉄不純物濃度に依存する傾向が見られた。さらに興味深いことに、ΔはBiO面の変調構造とも相関することがわかった。従来の超伝導体では不純物によりΓが大きくなり（寿命が短くなり）、これによりΔが抑制されるが、Bi2212ではΓに加え、CuO面外のディスオーダーもΔの抑制に寄与していると考えられる。これらの結果から、エネルギーギャップの大きさはCuO面間のカップリングや面外のディスオーダーに敏感であると考えられ、電子対の形成には面内の相互作用だけでなく面間のカップリングも重要な役割を果たしていると結論した。室蘭工業大学 (Muroran Institute of Technology)博士（工学

A line-of-sight electron cyclotron emission receiver for electron cyclotron resonance heating feedback control of tearing modes

An electron cyclotron emission (ECE) receiver inside the electron cyclotron resonance heating (ECRH) transmission line has been brought into operation. The ECE is extracted by placing a quartz plate acting as a Fabry¿Perot interferometer under an angle inside the electron cyclotron wave (ECW) beam. ECE measurements are obtained during high power ECRH operation. Thisdemonstrates the successful operation of the diagnostic and, in particular, a sufficient suppression of the gyrotron component preventing it from interfering with ECE measurements. When integratedinto a feedback system for the control of plasma instabilities this line-of-sight ECE diagnosticremoves the need to localize the instabilities in absolute coordinates

Impurity Effects on the Energy Gap in Fe-doped Bi2212

We performed scanning tunnelling microscopy/spectroscopy (STM/STS) on Fe-doped Bi2212. The Fe substitution for Cu causes a strong spatial inhomogeneity in STS spectra. The energy gap (Δ1 ∼80mV) has a sub-gap (Δ2 ∼70mV) in some distinct locations on the sample surface. We find that the gap edge peaks are largely depressed and only the sub-gap survives across the region where the spatial modulation of the local density of states is stronger. This indicates, that Δ1 anti-correlates with Δ2.Conference : 20th International Conference on Magnetism, ICM 2015Location : Barcelona, SPAINDate : JUL 05-10, 201

Validation of theory-based models for the control of plasma currents in W7-X divertor plasmas

A theory-based model for the control of plasma currents for steady-state operation in W7-X is proposed and intended for model-based plasma control. The conceptual outline implies the strength of physics-based models: it offer approaches applicable to future conditions of fusion devices or next-step machines. The application at extrapolated settings is related to the validity range of the theory model. Therefore, the predictive power of theory-based control models could be larger than for data-driven approaches and limitations can be predicted from the validity range for the prediction of bootstrap currents in W7-X. The model predicts the L/R response when density or heating power is changed. The model is based on neoclassical bootstrap current calculations and validated for different discharge conditions. While the model was found to be broadly applicable for conducted electron-cyclotron-heated discharges in W7-X, limits were found for cases when the polarization of the electron cyclotron heating was changed from X2 to O2-heating. The validity assessment attempts to quantify the potential of the derived model for model-based control in the operational space (density, heating power) of W7-X

Maternal and paternal genomes differentially affect myofibre characteristics and muscle weights of bovine fetuses at midgestation

Postnatal myofibre characteristics and muscle mass are largely determined during fetal development and may be significantly affected by epigenetic parent-of-origin effects. However, data on such effects in prenatal muscle development that could help understand unexplained variation in postnatal muscle traits are lacking. In a bovine model we studied effects of distinct maternal and paternal genomes, fetal sex, and non-genetic maternal effects on fetal myofibre characteristics and muscle mass. Data from 73 fetuses (Day153, 54% term) of four genetic groups with purebred and reciprocal cross Angus and Brahman genetics were analyzed using general linear models. Parental genomes explained the greatest proportion of variation in myofibre size of Musculus semitendinosus (80–96%) and in absolute and relative weights of M. supraspinatus, M. longissimus dorsi, M. quadriceps femoris and M. semimembranosus (82–89% and 56–93%, respectively). Paternal genome in interaction with maternal genome (P<0.05) explained most genetic variation in cross sectional area (CSA) of fast myotubes (68%), while maternal genome alone explained most genetic variation in CSA of fast myofibres (93%, P<0.01). Furthermore, maternal genome independently (M. semimembranosus, 88%, P<0.0001) or in combination (M. supraspinatus, 82%; M. longissimus dorsi, 93%; M. quadriceps femoris, 86%) with nested maternal weight effect (5–6%, P<0.05), was the predominant source of variation for absolute muscle weights. Effects of paternal genome on muscle mass decreased from thoracic to pelvic limb and accounted for all (M. supraspinatus, 97%, P<0.0001) or most (M. longissimus dorsi, 69%, P<0.0001; M. quadriceps femoris, 54%, P<0.001) genetic variation in relative weights. An interaction between maternal and paternal genomes (P<0.01) and effects of maternal weight (P<0.05) on expression of H19, a master regulator of an imprinted gene network, and negative correlations between H19 expression and fetal muscle mass (P<0.001), suggested imprinted genes and miRNA interference as mechanisms for differential effects of maternal and paternal genomes on fetal muscle.Ruidong Xiang, Mani Ghanipoor-Samami, William H. Johns, Tanja Eindorf, David L. Rutley, Zbigniew A. Kruk, Carolyn J. Fitzsimmons, Dana A. Thomsen, Claire T. Roberts, Brian M. Burns, Gail I. Anderson, Paul L. Greenwood, Stefan Hiendlede

Quantitative Evaluation of Neurite Morphology Using Graph Structure

Recently, the analysis of cellular images, particularly the assessment of neurite activity, has gained increasing significance in the study of neurodegenerative diseases, including Alzheimer’s disease. This study introduces an automated analysis approach that focuses on neurite activity through the application of cellular segmentation techniques to bright-field images of neurons. This study proposes a method for treating individual cell instances as graphs consisting of nodes and edges. Furthermore, this study suggests a quantitative assessment for precisely identified neurites through the definition of several evaluation metrics. This approach enables the fast and objective automated analysis of bright-field images focused on neurons. In a variety of experiments, the precision of our proposed method was verified through a comparative analysis by comparing the results to manual analysis data using ImageJ for measuring the neurite length of rat adrenal pheochromocytoma PC12 cells. The findings revealed that the average discrepancy in the length of neurites is only 4.387 μm, highlighting the high level of accuracy in our method’s ability to detect neurites, which is almost on par with manual analysis. This observation holds significance in analytical applications pertinent to Alzheimer’s disease