Low-Noise YBa_2Cu_3O_7-x dc SQUIDs Operating in Ambient Magne tic Fields
Abstract
The power spectrum of the 1/f flux noise S_Φ(f) of square washer thin film YBa_2Cu_3O_7-x (YBCO) dc SQUIDs generally scales linearly with the magnetic field B0 in which the device is cooled. The increase is due to the thermally activated hopping of flux vortices frozen into the film during cooling, and significantly limits the performance of high-Tc SQUIDs and magnetometers in ambient fields. We have found that reducing the linewidth of the SQUID loop to a value smaller than approximately (Φ_0/B_0)^1/2 eliminates the excess 1/f noise. Subsequently we fabricated SQUIDs that can be field-cooled without an increase in noise but that also couple efficiently to planar multiturn input coils. In these SQUIDs the washer is interpenetrated by an array of empty slots or holes so that the remaining YBCO is in the form of narrow linewidths, typically 4 μm wide. The flux noise of these SQUIDs at 1 Hz does not increase when the devices are cooled in fields of up to 130 μT, well above the earth's magnetic field. Thus, these narrow-linewidth configurations enable one to operate high-Tc magnetometers in a magnetically unshielded environment without a significant increase in the low frequency noise.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1997
- Bibcode:
- 1997APS..MAR.K2003D