Superconductivity in the Filled Cage Compounds Ba6Ge25 and Ba4Na2Ge25
F. M. Grosche, H. Q. Yuan, W. Carrillo-Cabrera, S. Paschen, C. Langhammer, F. Kromer, G. Sparn, M. Baenitz, Yu. Grin, F. Steglich
DOI 10.1103/PhysRevLett.87.247003 · Physical Review Letters
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Abstract
The clathrate compound Ba6Ge25 and its relatives consist of a rigid germanium skeleton, into which barium or other metal atoms are coordinated. These guest atoms can “rattle” freely at high temperatures, but in Ba6Ge25 some of them lock randomly into split positions below TS∼200K. The resulting bad metal undergoes a BCS-like superconducting transition at Tc≃0.24K. Tc increases more than 16-fold, as TS is suppressed by hydrostatic pressure p, but changes only slightly with p from Tc≃0.84K in the undistorted sister compound Ba4Na2Ge25. The large enhancement of Tc in Ba6Ge25 may be attributed mainly to the pressure tuning of strong disorder caused by the random displacement of Ba atoms at TS.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Ba6Ge25 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 0.24 | Pressure unresolved | midpoint |
| Ba6Ge25 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 0.14 | Pressure unresolved | unknown |
| Ba6Ge25 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 3.8 | 2.7 GPa | midpoint |
| Ba4Na2Ge25 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 0.84 | Pressure unresolved | unknown |
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