Strong Quantum Fluctuations In 400 Angstrom Thick Ybco Thin Films

Magnetic relaxation and I-V characteristics in 400 Angstrom thick epitaxial Y1B2C3O films have been measured down to 1.5K. It was found that the normalized magnetic relaxation rates become independent of temperature below 9 K in an applied field of 8Oe, meanwhile the I-V characteristics can be well described by macroscopic quantum tunneling theory up to 4.2k in an applied magnetic field of 6T. These facts reveal strong quantum fluctuations in these ultrathin films.