Quantum tunneling effects in YBa2Cu3Ox superthin films

Magnetic relaxation and V-I characteristics in 60 Angstrom thick YBCO super -thin films have been measured. The normalized relaxation rates and the slo pes of Ig(V)-I curves in an applied field up to 6 T become independent of t emperature below 16 IC. This fact indicates that the temperature T-er at wh ich the Vortex dynamics changes from thermal activation to quantum tunnelin g can be much higher than those reported previously. Analysis of experiment al results suggests that the high pinning energy in YBCO super-thin films i s an important factor that contributes to a high T-er. (C) 2000 Elsevier Sc ience B.V. All rights reserved.