Magnetic relaxation study of macroscopic quantum tunnelling in YBCO films

Magnetic relaxation and I-V characteristics of YBCO films with a thickness ranging from 2.4 to 200 nm have been studied. Magnetic relaxation measurements show strong quantum tunnelling effects at temperatures as high as T-cr = 8.5-15 K in ultra-thin films (2.4-40 nm), whereas in 200 nm film it is dominated by thermal activation down to 4.2 K. The high T-cr of ultra-thin films is interpreted using Blatter's dissipative tunnelling theory. The strong quantum fluctuations in the ultra-thin films are explained by their large normal state resistivity and higher activation energy compared to thicker films.Physics, AppliedPhysics, Condensed MatterSCI(E)EI2ARTICLE91300-13031