Low magnetic flux noise observed in laser-deposited in situ films of YB2Cu3Oy and implications for high- Tc SQUIDs

Abstract

THE first device made from a thin film of a high-transition-temperature (high-Tc) superconductor was a d.c. SQUID (superconducting quantum interference device)1. Many applications of SQUIDs demand high sensitivity at low frequencies f( ≤1 Hz), and thus require films with low intrinsic '1/f magnetic flux noise2, 3. Although the level of 1/f noise in T2Ba2Ca2Cu3Ox SQUIDs4 is significantly lower than that in earlier YBa2Cu3O3, (YBCO) SQUIDs1, it remains higher than that in low-Tc devices. In post-annealed films of YBCO, the magnitude of the 1/f noise has been shown5 to decrease dramatically as the quality of the films is improved. Here we report measurements of flux noise in a film of YBCO grown in situ by pulsed laser deposition (but not patterned into a SQUID). The 1/f noise level was two orders of magnitude lower than in our best post-annealed film. Provided that it proves possible to fabricate suitable low-noise Josephson junctions, a d.c. SQUID made from a film of this quality and operated at liquid-nitrogen temperature (77 K) should approach the low-frequency performance currently achieved in commerically available Iow-Tc SQUIDs.