We study the effects of hydrostatic pressure (HP) compression on the superconducting transition of severely strained Nb samples, whose grain sizes are reduced to the submicrometer level. Engineered granularity by high-pressure torsion (HPT) treatment changes the strength of coupling between submicrometer-scale grains and introduces lattice strain. We attempt to utilize the initially accumulated shear strain in the starting material for increasing the superconducting transition temperature under HP compression. The HP effects on non-strained Nb have already been investigated in the pressure regime over 100 GPa by Struzhkin et al. [Phys. Rev. Lett. , 4262 (1997)], and reportedly exhibited an increase from 9.2 to 9.9 K at approximately 10 GPa. (1) Slightly strained Nb in the HPT treatment exhibits the increase in under HP due to the strengthening of the intergrain coupling, so the pressure scale of the pressure response observed by Struzhkin et al. is reduced to approximately one-seventh at the maximum. (2) Prominently strained Nb in the HPT treatment exhibits the increase in under HP due to a reduction in structural symmetry at the unit-cell level: In a Nb sample subjected to HPT (6 GPa, 10 revolutions), exceeds 9.9 K at approximately 2 GPa. According to our first-principle calculations, the reduction in the structural symmetry affords an increase in the density of states at the Fermi energy, thereby yielding a prominent increase in at low pressures.
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28 March 2019
Research Article|
March 22 2019
Hydrostatic pressure effects on superconducting transition of nanostructured niobium highly strained by high-pressure torsion
Masaki Mito;
Masaki Mito
a)
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Yuichiro Kitamura;
Yuichiro Kitamura
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Takayuki Tajiri;
Takayuki Tajiri
2
Faculty of Science, Fukuoka University
, Fukuoka 814-0180, Japan
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Kazuma Nakamura;
Kazuma Nakamura
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Ryo Shiraishi;
Ryo Shiraishi
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Kazuma Ogata;
Kazuma Ogata
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Hiroyuki Deguchi;
Hiroyuki Deguchi
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Tomiko Yamaguchi;
Tomiko Yamaguchi
1
Graduate School of Engineering, Kyushu Institute of Technology
, Kitakyushu 804-8550, Japan
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Nao Takeshita;
Nao Takeshita
3
National Institute of Advanced Industrial Science and Technology
, Tsukuba 305-8568, Japan
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Terukazu Nishizaki;
Terukazu Nishizaki
4
Department of Electrical Engineering, Kyushu Sangyo University
, Fukuoka 813-8503, Japan
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Kaveh Edalati;
Kaveh Edalati
5
Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University
, Fukuoka 819-0395, Japan
6
International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University
, Fukuoka 819-0395, Japan
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Zenji Horita
Zenji Horita
5
Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University
, Fukuoka 819-0395, Japan
6
International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University
, Fukuoka 819-0395, Japan
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a)
Electronic address: mitoh@mns.kyutech.ac.jp
J. Appl. Phys. 125, 125901 (2019)
Article history
Received:
November 28 2018
Accepted:
March 03 2019
Citation
Masaki Mito, Yuichiro Kitamura, Takayuki Tajiri, Kazuma Nakamura, Ryo Shiraishi, Kazuma Ogata, Hiroyuki Deguchi, Tomiko Yamaguchi, Nao Takeshita, Terukazu Nishizaki, Kaveh Edalati, Zenji Horita; Hydrostatic pressure effects on superconducting transition of nanostructured niobium highly strained by high-pressure torsion. J. Appl. Phys. 28 March 2019; 125 (12): 125901. https://doi.org/10.1063/1.5083094
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