Journal
JOURNAL OF LOW TEMPERATURE PHYSICS
Volume 158, Issue 3-4, Pages 692-696Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s10909-009-9984-x
Keywords
NMR; Supersolid; Defects; Preamplifier
Categories
Funding
- NSF [DMR 0654118]
- State of Florida
- NHMFL
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Recent experimental studies of solid He-4 indicate a strong correlation between the crystal defects and the onset of a possible supersolid state. We use pulsed NMR techniques to explore the quantum dynamics of the He-3 impurities in the solid He-4 in order to examine certain theoretical models that describe how the disordered states are related to supersolidity. Because of the very small signal-to-noise ratio at low He-3 concentration and the long spin-lattice relaxation time (T (1)), it is essential to significantly enhance the NMR sensitivity to be able to carry out the experiments. Here we present the design of a novel low temperature preamplifier which is built with a low noise pseudomorphic HEMT transistor that is embedded into a cross-coil NMR probe. With a low power dissipation of about 0.7 mW, the preamplifier is capable of providing a power gain of 30 dB. By deploying the preamplifier near the NMR coil below 4 K, the noise temperature of the receiver is reduced to approximately 1 K. This preamplifier design also has the potential to be adapted into a low temperature amplifier with both input and output impedance at 50 Omega or a low temperature oscillator.
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