title: Large enhancement of superconducting transition temperature of SrBi3 induced by Na substitution for Sr.
abstract: The Matthias rule, which is an empirical correlation between the superconducting transition temperature (Tc) and the average number of valence electrons per atom (n) in alloys and intermetallic compounds, has been used in the past as a guiding principle to search for new superconductors with higher Tc. The intermetallic compound SrBi3 (AuCu3 structure) exhibits a Tc of 5.6 K. An ab-initio electronic band structure calculation for SrBi3 predicted that Tc increases on decreasing the Fermi energy, i.e., on decreasing n, because of a steep increase in the density of states. In this study, we demonstrated that high-pressure (~ 3 GPa) and low-temperature ( < 350 °C) synthesis conditions enables the substitution of Na for about 40 at.% of Sr. With a consequent decrease in n, the Tc of (Sr,Na)Bi3 increases to 9.0 K. A new high-Tc peak is observed in the oscillatory dependence of Tc on n in compounds with the AuCu3 structure. We have shown that the oscillatory dependence of Tc is in good agreement with the band structure calculation. Our experiments reaffirm the importance of controlling the number of electrons in intermetallic compounds.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Iyo
authors.affiliation: 1] National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan [2] IMRA Material R&D Co., Ltd., 2-1 Asahi-machi, Kariya, Aichi 448-0032, Japan.
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Yanagi
authors.affiliation: 1] National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan [2] Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Kinjo
authors.affiliation: 1] National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan [2] Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan.
authors.forename: Taichiro
authors.initials: T
authors.lastname: Nishio
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Hase
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yanagisawa
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Ishida
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Hijiri
authors.initials: H
authors.lastname: Kito
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Nao
authors.initials: N
authors.lastname: Takeshita
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Oka
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Yoshida
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Eisaki