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Journal Articles

Anomalous vortex dynamics in the spin-triplet superconductor UTe$$_2$$

Tokiwa, Yoshifumi; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Yanase, Yoichi*; Haga, Yoshinori; et al.

Physical Review B, 108(14), p.144502_1 - 144502_5, 2023/10

The vortex dynamics in the spin-triplet superconductor, UTe$$_2$$, are studied by measuring the DC electrical resistivity with currents along the $$a$$-axis under magnetic fields along the $$b$$-axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.

Journal Articles

Field induced multiple superconducting phases in UTe$$_2$$ along hard magnetic axis

Sakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori

Physical Review Letters, 130(19), p.196002_1 - 196002_6, 2023/05

 Times Cited Count:0 Percentile:90.46(Physics, Multidisciplinary)

The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields ($$H$$) along the hard magnetic $$b$$-axis using a high-quality single crystal with $$T_{rm c}$$ = 2.1 K. Simultaneous electrical resistivity and AC magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the $$H^{ast}$$ of $$sim15$$ T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near $$H^{ast}$$, indicating an intermediate SC phase characterized by small flux pinning forces.

Journal Articles

Flux pinning properties of correlated pinning at low temperatures in ErBCO films with inclined columnar defects

Awaji, Satoshi*; Namba, Masashi*; Watanabe, Kazuo*; Kai, Hideki*; Mukaida, Masashi*; Okayasu, Satoru

Journal of Applied Physics, 111(1), p.013914_1 - 013914_4, 2012/01

 Times Cited Count:24 Percentile:69.68(Physics, Applied)

The effect of $$c$$-axis correlated pinning on the critical current density $$J$$$$_{c}$$ at low temperatures under high magnetic fields was investigated on the basis of the transport measurements of $$J$$$$_{c}$$ and irreversibility field B$$_{irr}$$ properties of an ErBa$$_{2}$$Cu$$_{3}$$O$$_{y}$$ film with inclined columnar defects. The contribution of correlated pinning on $$J$$$$_{c}$$ decreased drastically with decreasing temperature under high magnetic fields above the matching field. At low temperatures, the presence of a matching field limited the pinning force for correlated pinning, while the ratio of the maximum pinning force of the correlated pinning to the random one was proportional to the inverse of B$$_{irr}$$. In order to improve the critical current properties at low temperatures under high magnetic fields, an increase in the matching field and/or the introduction of strong random pinning are effective.

Journal Articles

Cooperative behavior of the random and correlated pinning in Er123 films with columnar defects

Awaji, Satoshi*; Namba, Masashi*; Watanabe, Kazuo*; Ito, Shun*; Aoyagi, Eiji*; Kai, Hideki*; Mukaida, Masashi*; Okayasu, Satoru

IEEE Transactions on Applied Superconductivity, 21(3), p.3192 - 3195, 2011/06

 Times Cited Count:5 Percentile:33.82(Engineering, Electrical & Electronic)

The flux pinning behaviors for the heavy ion irradiated Er123 films are investigated based on the detailed $$J$$$$_{rm c}$$ ($$B$$, $$T$$, $$theta$$) properties. The double peaks of $$F$$$$_{rm p}$$ curves for $$B$$//c appear in case of the matching field of 0.3 T along $$c$$-axis and 1.7 T tilted from $$c$$-axis. In addition, the peaks on $$J$$$$_{rm c}$$ ($$theta$$) at $$theta$$ = 0$$^{circ}$$ (B//c), which originate from the columnar defects, decrease with increasing magnetic field but increase again near the irreversibility field. We found that the cooperation model of the $$c$$-axis correlated and random pinning centers can describe the observed double peak behavior of $$F$$$$_{rm p}$$(B) and the angular dependence of $$J$$$$_{rm c}$$ related to the correlated pinning.

Journal Articles

Stress/strain effects on industrial superconducting composites

Ito, Takayoshi; Harjo, S.; Osamura, Kozo*; Hemmi, Tsutomu; Awaji, Satoshi*; Machiya, Shutaro*; Oguro, Hidetoshi*; Nishijima, Gen*; Takahashi, Koki*; Matsui, Kunihiro; et al.

Materials Science Forum, 681, p.209 - 214, 2011/05

 Times Cited Count:1 Percentile:52.96

Journal Articles

Performance tests of reactor containment structures of the HTTR

Iigaki, Kazuhiko; Sakaba, Nariaki; Kawaji, Satoshi; Iyoku, Tatsuo

Transactions of 16th International Conference on Structural Mechanics in Reactor Technology (SMiRT-16) (CD-ROM), 7 Pages, 2001/08

no abstracts in English

Journal Articles

Instrumentation and control system of the HTTR

Saito, Kenji; Homma, Fumitaka; Omata, Toru; Aono, Tetsuya; Kawaji, Satoshi; Kawasaki, Kozo; Iyoku, Tatsuo

Proceedings of International Topical Meeting on Nuclear Plant Instrumentation, Controls, and Human-Machine Interface Technologies (NPIC&HMIT 2000) (CD-ROM), 8 Pages, 2000/00

no abstracts in English

JAEA Reports

Countermeasure to prevent temperature rise of primary upper shield in HTTR; Additional countermeasures and their performance test

Tachibana, Yukio; Kunitomi, Kazuhiko; *; Sawa, Kazuhiro; Takeda, Takeshi; Saikusa, Akio; Kawaji, Satoshi; Iyoku, Tatsuo

JAERI-Tech 98-027, 74 Pages, 1998/07

JAERI-Tech-98-027.pdf:2.23MB

no abstracts in English

JAEA Reports

Performance tests of the reactor containment structures of HTTR

Sakaba, Nariaki; Iigaki, Kazuhiro; Kawaji, Satoshi; Iyoku, Tatsuo

JAERI-Tech 98-013, 152 Pages, 1998/03

JAERI-Tech-98-013.pdf:7.69MB

no abstracts in English

Journal Articles

Design and present status of high-temperature engineering test reactor

Baba, Osamu; Kunitomi, Kazuhiko; Kawaji, Satoshi; Tanaka, Toshiyuki; Shiozawa, Shusaku; Okubo, Minoru

Proc. of ASME$$cdot$$JSME 4th Int. Conf. on Nuclear Engineering 1996 (ICONE-4), 2, p.281 - 287, 1996/00

no abstracts in English

Journal Articles

Application and working characteristics of HTGR components test machines with magnetic bearings

Shimomura, Hiroaki; Kawaji, Satoshi; Ota, Yukimaru

Proc. of the 2nd Int. Symp. on Magnetic Bearings, p.93 - 99, 1990/00

no abstracts in English

Journal Articles

Application and experience of distributed control systems and coupled computer network in HTGR development facility

Shimomura, Hiroaki; Kawaji, Satoshi

Proc. of the IAEA Specialists' Meeting on Communication and Data Transfer in NPP, 17 Pages, 1990/00

no abstracts in English

JAEA Reports

A Study on shaft vibration of gas circulators with gas-bearing for HENDEL test facility

Shimomura, Hiroaki; Kawaji, Satoshi; Fujisaki, Katsuo;

JAERI-M 89-064, 90 Pages, 1989/06

JAERI-M-89-064.pdf:3.71MB

no abstracts in English

Journal Articles

Operating experience on gas bearing helium circulators in HTGR development facility

Shimomura, Hiroaki; Kawaji, Satoshi; Fujisaki, Katsuo;

Gas-Cooled Reactor Coolant Circulator and Blower Technology, p.148 - 156, 1988/00

no abstracts in English

Oral presentation

Engineering materials diffractometer "TAKUMI" and stress/strain effects on industrial superconducting composites

Harjo, S.; Aizawa, Kazuya; Ito, Takayoshi; Osamura, Kozo*; Awaji, Satoshi*; Hemmi, Tsutomu; Machiya, Shutaro*; Tsuchiya, Yoshinori*; Matsui, Kunihiro; Nishijima, Gen*

no journal, , 

no abstracts in English

Oral presentation

Internal strain measurement in superconducting composites by neutron diffraction

Harjo, S.; Aizawa, Kazuya; Ito, Takayoshi*; Abe, Jun; Osamura, Kozo*; Hemmi, Tsutomu; Jin, X.*; Nakamoto, Tatsushi*; Awaji, Satoshi*; Takahashi, Koki*

no journal, , 

Oral presentation

Magnetic fluctuations in strongly correlated $$f$$ electrons system URu$$_2$$Si$$_2$$ under high fields

Sakai, Hironori; Higa, Nonoka; Hattori, Taisuke; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Goto, Takayuki*; Hirata, Michihiro*; Awaji, Satoshi*; Sasaki, Takahiko*

no journal, , 

We have performed $$^{29}$$Si nuclear magnetic resonance (NMR) experiments using single crystal of strongly correlated $$5f$$ electrons system URu$$_2$$Si$$_2$$ under high external field of about 24 T. The temperature dependence of NMR shift in the paramagnetic state varies with external fields. The temperature and field dependences of NMR shifts resembles those of magnetic susceptibility.

Oral presentation

Magnetic entropy of UTe$$_2$$

Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; et al.

no journal, , 

UTe$$_2$$ has attracted much attention due to the possibility of reentrant superconductivity and spin triplet superconductivity in a magnetic field. In this material, when a magnetic field is applied in the b-axis direction, Tc decreases once due to the magnetic field, but Tc increases under a magnetic field of about 16T or more. In this field direction, there is a metamagnetic transition at 34T. The relationship between this metamagnetism and the anomalous enhancement of Tc has been discussed. Many unconventional superconductors exhibit an unusual metallic state in the normal phase. It is believed that magnetic fluctuations, which are the cause of this phenomenon, generate superconducting electron pairs. Entropy is a direct measure of fluctuations, as entropy exhibits a maximum at the quantum critical point. Therefore, the relationship between fluctuations and superconductivity can be clarified by entropy measurements in the normal state. In this study, we performed precise magnetization measurements at temperatures up to 2 K and magnetic fields up to 24 T using cryogen-free superconducting magnets at the Research Center for High Magnetic Field Superconducting Materials, IMR, Tohoku University. We used a thermodynamic relation to map the entropy in the magnetic field-temperature parameter space. In this talk, we discuss the relationship between the entropy increase due to metamagnetic fluctuations and superconductivity.

Oral presentation

Superconducting upper critical fields in high-quality single crystals of UTe$$_2$$

Haga, Yoshinori; Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo; Kimata, Motoi*; Nakamura, Shintaro*; Awaji, Satoshi*; et al.

no journal, , 

no abstracts in English

Oral presentation

Magnetic field-temperature phase diagram along the magnetic hard axis for spin-triplet superconductor UTe$$_2$$

Sakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori

no journal, , 

For a paramagnetic superconductor UTe$$_2$$, a "field-reionforced superconducting state" in which $$T_{rm c}$$ increases with magnetic field above 15 T emerges when a magnetic field is applied "exactly" in the direction of the magnetically hard $$b$$ axis. In order to investigate this high-field superconducting phase, we have attempted to determine the magnetic field-temperature phase diagram of ultra-clean single crystals using a cryogen-free 25 T superconducting magnet (25T-CSM) at the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. In this presentation, we will report the obtained results.

29 (Records 1-20 displayed on this page)