DEHAAS-VANALPHEN EFFECT IN SUPERCONDUCTORS BELOW BC2

The de Haas van Alphen effect has been investigated in YBCO recently by Fowler et al. using 100 Tesla fields and temperatures below 4.2 K. It is conclude-d that even at these fields these measurements were taken below the superconducting critical field, Bc2. Similar effects have been seen by Graebner and Robins in NbSe2 in 1976 and more recently by Mueller, Lowndes, and Arko et al. in V3Si. The implication,of such mixed state experiments is discussed.