Phys Rev B Condens Matter
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Phys Rev B Condens Matter
May 1991
Phys Rev B Condens Matter
November 1990
Phys Rev B Condens Matter
June 1990
Phys Rev B Condens Matter
September 1989
Phys Rev B Condens Matter
November 1988
Phys Rev B Condens Matter
September 1988
Phys Rev B Condens Matter
June 1988