= Helium-3 superfluid discovery experiment
<David Morris Lee>, <Douglas Dean Osheroff> and <Robert Coleman Richardson> compressed coexisting <liquid> and <solid> <helium-3> in a cell precooled by a <dilution refrigerator>. <Helium-4> <pressure> drove coupled bellows and a piston; a <capacitance diaphragm gauge> read <pressure> and platinum <nuclear magnetic resonance> supplied thermometry. Uniform compression revealed a slope break A and a small <pressure> drop B; decompression and varied <solid> fraction checked reproducibility. Their April 1972 paper, Evidence for a New Phase of Solid He3, interpreted a new <solid> phase, without establishing liquid <superfluidity>. <Evidence for a New Phase of Solid He3 by Douglas Dean Osheroff and others>[1972, pp.885–888, Figs.1–3]{ref}
The October follow-up replaced the thermometer assembly with a sample <nuclear magnetic resonance> coil. An applied <magnetic field> <gradient> selected different sample layers, separating strong <solid> signals from the <liquid> background. At A the <liquid> resonance shifted; at B its shift disappeared and its <magnetic susceptibility> fell. Removing the <gradient> resolved the frequency shift directly. Independence from <solid> fraction and distinct relaxation times supported the <liquid> assignment. Thus the reinterpretation rested on phase-selective evidence, rather than relabeling the first paper's title. These magnetic observations identify changed <liquid> phases; they do not directly measure frictionless flow. <New Magnetic Phenomena in Liquid He3 below 3 mK by Douglas Dean Osheroff and others>[1972, pp.920–923, Figs.1–3]{ref}
<Douglas Dean Osheroff> recalls the subsequent p-wave interpretation. <Superfluidity in 3He: Discovery and Understanding by Douglas Dean Osheroff>[1996 lecture, p.73]{ref}
\Image[/helium-three-compression-cell-readout.png]
{title=Compression and independent readout channels in the <helium-3 superfluid discovery experiment>}
{description=Original functional diagram, not a reconstruction to scale. Left: drive, sample and <pressure> channel. Right: separate thermometer and sample <nuclear magnetic resonance> configurations; the latter replaces the former in the follow-up. Connections indicate function, not historical wiring.}
The inference has a useful limit. A <pressure> anomaly in two coexisting phases cannot, by itself, identify which phase changed: both contribute to the common <phase coexistence curve>. Thermometer lag, a <temperature> <gradient> or slow equilibration can also separate indicated <temperature> from the sample state. Correlating another response with the anomaly provides information that repeating the same <pressure> trace cannot supply. Conversely, a shifted magnetic resonance alone does not measure a frictionless flow rate.
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