Stabilizing a SQUID-based amplifier in high magnetic fields
ORAL
Abstract
dc SQUID-based circuits, when connected to sources exposed to strong magnetic fields, are often unstable in their fluxed-locked mode. We present a low noise SQUID-based current amplifier, which is unconditionally stable with a source exposed to magnetic fields up to 10 T.
Stability is achieved by inserting a four-pole low-pass filter between the source and the current
amplifier. With this circuit, we demonstrate Johnson noise measurements below 1 K for source
impedances in the kΩ range subjected to strong magnetic fields. We also discuss preliminary
high-resolution thermal transport data in a two-dimensional electron gas confined in GaAs/AlGaAs.
Stability is achieved by inserting a four-pole low-pass filter between the source and the current
amplifier. With this circuit, we demonstrate Johnson noise measurements below 1 K for source
impedances in the kΩ range subjected to strong magnetic fields. We also discuss preliminary
high-resolution thermal transport data in a two-dimensional electron gas confined in GaAs/AlGaAs.
*The work at Purdue was supported by the NSF grant DMR-1505866. L.N.P. and K.W.W.
acknowledge the Gordon and Betty Moore Foundation Grant No. GBMF 4420, and the National Science Foundation
MRSEC Grant No. DMR-1420541.
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Presenters
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Vidhi Shingla
- Purdue University