Penetration depth measurements of YBa2Cu3O/sub 7-delta/ at 4 MHz

Measurements were made of the penetration depth of bulk and powder samples of YBa sub 2 Cu sub 3 O sub 7-delta. The samples were placed in an inductor which was part of the resonant circuit of a 4 MHz tunnel diode oscillator. The oscillator was stable to at least 1 part in 10 at 77 K. Changes in the sample susceptibility were easily detected by changes in the oscillator frequency. Analysis of the smallest powders fabricated gave a value of the measured penetration depth lambda sub mea = 0.23 microns. The measurement methodology is quantitative and the value of lambda sub mea is believed to be an upper bound of the true penetration depth.