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.

Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi3 (A = Sr and Ba)

“…Few people have realized that SOC should influence the superconductivity of those compounds in the past years. Very recently, ABi 3 (A=Sr and Ba) were reinvestigated 18,19 . Haldolaarachchige et al prepared the single crystal sample of BaBi 3 and concluded the physical parameters in detail 18 .…”

“…Haldolaarachchige et al prepared the single crystal sample of BaBi 3 and concluded the physical parameters in detail 18 . Iyo et al investigated superconductivity in polycrystalline sample of Na doped SrBi 3 19 . However, the role of SOC still has not been discussed.…”

“…Few people have realized that SOC should influence the superconductivity of those compounds in the past years. Very recently, ABi 3 (A = Sr and Ba) were reinvestigated1819. Haldolaarachchige et al .…”

“…Iyo et al . investigated superconductivity in polycrystalline sample of Na doped SrBi 3 19. However, the role of SOC still has not been discussed.…”

Superconductivity in CaBi2

“…There are several bismuthalkaline and alkaline-earth metal intermetallic superconductors known, including LiBi [6], NaBi [7], KBi 2 [8], RbBi 2 , CsBi 2 [9], Ca 11 Bi 10-x [10], SrBi 3 [11,12], BaBi 3 [13], and Ba 2 Bi 3 [14]. Recently, intermetallic phases in the Ca-Bi chemical system were examined using theoretical calculations, and three potential superconductors were proposed: CaBi 3 , CaBi, and Ca 3 Bi [15].…”