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Journal Articles

Metallization and pressure-induced superconductivity in carrier doped excitonic insulator (Ta$$_{1-x}$$Ti$$_x$$)$$_2$$NiSe$$_5$$

Tsuchida, Shun*; Hirose, Yusuke; Sekikawa, Takuya; Ono, Yoshiaki*; Hirahara, Takuya*; Sano, Sumika*; Kawaguchi, Shogo*; Kobayashi, Shintaro*; Uwatoko, Yoshiya*; Settai, Rikio*

Journal of the Physical Society of Japan, 94(11), p.114703_1 - 114703_7, 2025/10

 Times Cited Count:2 Percentile:51.84(Physics, Multidisciplinary)

We investigated the carrier doping effect on an excitonic insulator Ta$$_2$$NiSe$$_5$$ by means of the electrical resistivity $$rho$$ and Hall coefficient $$R_{rm H}$$ using single crystals of (Ta$$_{1-x}$$Ti$$_x$$)$$_2$$NiSe$$_5$$, and band calculation. The excitonic transition temperature $$T_{rm c}$$ is continuously suppressed to 83 K at $$x$$ = 0.104 while preserving the crystal structure. With increasing substitution concentration $$x$$, a semiconducting increment of $$rho$$ and $$R_{rm H}$$ is strongly suppressed and a metallic behavior is observed at $$x$$ > 0.06. Ti substitution can realize an excitonic correlated metallic state. This metallization is explained by the hole doping effect based on the band calculations. Applying pressure to the carrier doped (Ta$$_{1-x}$$Ti$$_x$$)$$_2$$NiSe$$_5$$, we found superconductivity above 2.6 GPa, which is much smaller than that of Ta$$_2$$NiSe$$_5$$ around 8 GPa. The carrier doping induced by Ti substitution favors superconductivity in this compound.

JAEA Reports

Japan - IAEA Joint Nuclear Energy Management School 2016

Yamaguchi, Mika; Hidaka, Akihide; Ikuta, Yuko; Murakami, Kenta*; Tomita, Akira*; Hirose, Hiroya*; Watanebe, Masanori*; Ueda, Kinichi*; Namaizawa, Ken*; Onose, Takatoshi*; et al.

JAEA-Review 2017-002, 60 Pages, 2017/03

JAEA-Review-2017-002.pdf:9.41MB

Since 2010, IAEA has held the NEM School to develop future leaders who plan and manage nuclear energy utilization in their county. Since 2012, JAEA together with Japan Nuclear HRD Network, University of Tokyo, Japan Atomic Industrial Forum and JAIF International Cooperation Center have cohosted the school in Japan in cooperation with IAEA. Since then, the school has been held in Japan every year. In 2006, Japanese nuclear technology and experience, such as lessons learned from the Fukushima Daiichi Nuclear Power Plant accident, were provided to offer a unique opportunity for the participants to learn about particular cases in Japan. Through the school, we contributed to the internationalization of Japanese young nuclear professionals, development of nuclear human resource of other countries including nuclear newcomers, and enhanced cooperative relationship with IAEA. Additionally, collaborative relationship within the network was strengthened by organizing the school in Japan.

Journal Articles

Development of 7 T Cryogen-free superconducting magnet for gyrotron

Hirose, Ryoichi*; Kamikado, Takeshi*; Okui, Yoshio*; Miyata, Hitoshi*; Shibutani, Kazuyuki*; Ozaki, Osamu*; Sakamoto, Keishi

IEEE Transactions on Applied Superconductivity, 18(2), p.920 - 923, 2008/06

 Times Cited Count:17 Percentile:62.64(Engineering, Electrical & Electronic)

A special type of 7 T 240 mm vertical bore cryogen-free superconducting magnet system was developed. The magnet system consists of three sets of coils which are charged separately. A set of sweep coils are located inside of the main coil. The sweep coil produces only $$pm$$0.2 T but is charged and discharged within 10 seconds so as to control electron trajectory. To avoid quench with the rise of the temperature from the large AC loss, this set of coils are wound with Nb$$_{3}$$Sn conductor. This magnet system will contribute to the fast control of the gyrotron oscillation frequency.

Journal Articles

Characterization of surface carbon films on weathered Japanese roof tiles by soft X-ray spectroscopy

Muramatsu, Yasuji; Yamashita, Michiru*; Motoyama, Muneyuki*; Hirose, Mika*; Denlinger, J. D.*; Gullikson, E. M.*; Perera, R. C. C.*

X-Ray Spectrometry, 34(6), p.509 - 513, 2005/11

 Times Cited Count:1 Percentile:5.47(Spectroscopy)

Surface carbon films on the weathered Japanese roof tiles were characterized by soft X-ray spectroscopy. From the X-ray absorption measurements, it was confirmed that the surface carbon films were oxidized by weathering. On the ohterhand, from the X-ray emission measurements, it can be confirmed that the degree of the orientation was kept in the inner carbon films.

Oral presentation

Structural study of elemental substituted excitonic insulator Ta$$_{2}$$NiSe$$_{5}$$ using X-ray diffraction

Hirose, Yusuke; Tsuchida, Shun*; Sano, Sumika*; Kawaguchi, Shogo*; Kobayashi, Shintaro*; Omura, Ayako*; Settai, Rikio*

no journal, , 

Ta$$_{2}$$NiSe$$_{5}$$ undergoes a structural phase transition from orthorhombic to monoclinic at Tc~330K and simultaneously becomes an insulator, which attracts attention as one of candidate materials for exciton insulators, and has been actively studied. We have previously demonstrated that element substitution can suppress Tc and cause the system to become metallic. In this study, we aimed to clarify the origin of the change in electronic state due to element substitution by crystal structure analysis, and we performed powder X-ray diffraction experiments on element-substituted Ta$$_{2}$$NiSe$$_{5}$$ at BL02 of SPring-8, and we will report the results.

Oral presentation

None

Yamashita, Rio*; Tsuchida, Shun*; Sano, Sumika*; Hirose, Yusuke; Settai, Rikio*

no journal, , 

no abstracts in English

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