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Superconductivity in the filled cage compounds Ba6Ge25 and Ba4Na2Ge25.

Authors
  • Grosche, F M
  • Yuan, H Q
  • Carrillo-Cabrera, W
  • Paschen, S
  • Langhammer, C
  • Kromer, F
  • Sparn, G
  • Baenitz, M
  • Grin, Y
  • Steglich, F
Type
Published Article
Journal
Physical review letters
Publication Date
Dec 10, 2001
Volume
87
Issue
24
Pages
247003–247003
Identifiers
PMID: 11736532
Source
Medline
License
Unknown

Abstract

The clathrate compound Ba 6Ge25 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 Ba 6Ge25 some of them lock randomly into split positions below T(S) approximately 200 K. The resulting bad metal undergoes a BCS-like superconducting transition at T(c) approximately 0.24 K. T(c) increases more than 16-fold, as T(S) is suppressed by hydrostatic pressure p, but changes only slightly with p from T(c) approximately 0.84 K in the undistorted sister compound Ba 4Na2Ge25. The large enhancement of T(c) in Ba 6Ge25 may be attributed mainly to the pressure tuning of strong disorder caused by the random displacement of Ba atoms at T(S).

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