Anthony Clark

Nonclassical rotational inertia in helium crystals.

It has been proposed that the observed nonclassical rotational inertia (NCRI) in solid helium results from the superflow of thin liquid films along interconnected grain boundaries within the sample. We have observed NCRI in large (4)He crystals grown at constant temperature and pressure, demonstrating that the superfluid grain boundary model cannot explain the phenomenon.

Effect of 3He impurities on the nonclassical response to oscillation of solid 4He.

We have investigated the influence of impurities on the possible supersolid transition in 4He by systematically enriching isotopically pure samples with 3He. The addition of 3He broadens the onset of nonclassical rotational inertia and shifts it to higher temperature, suggesting that the phenomenon is correlated with the condensation of 3He atoms onto the dislocation network in solid 4He.

Probable heat capacity signature of the supersolid transition

Liquid 4He enters the superfluid state and flows without friction below 2.176 K. Thin liquid films adsorbed on solid substrates undergo the same transformation, although at a lower temperature. When the substrate is subjected to oscillatory motion a portion of the film, known as the superfluid fraction, decouples from the oscillation. A similar phenomenon has been observed in solid 4He, in which a fraction of the solid seems to decouple from the motion of the surrounding lattice. Although this observation has been replicated in various laboratories, no thermodynamic signature of the possible supersolid transition has been seen. Here we report the finding of a heat capacity peak that coincides with the onset of mass decoupling. This complementary experimental evidence supports the existence of a genuine transition between the normal solid and supersolid phases of 4He.

Thermal history of solid H 4 e under oscillation

We have studied the thermal history of the resonant frequency of a torsional oscillator containing solid

Heat capacity peak in solid 4He: effects of disorder and 3He impurities.

^{4}\text{H}\text{e}

Metallic Coulomb blockade thermometry down to 10 mK and below

. We find that the magnitude of the frequency shift that occurs below

Method for Cooling Nanostructures to Microkelvin Temperatures

\ensuremath{\sim}100\text{ }\text{mK}

Search for Superfluidity in Solid Hydrogen

is multivalued in the low-temperature limit, depending strongly on how the state is prepared. This result can be qualitatively explained in terms of the motion and pinning of quantized vortices within the sample. Several aspects of the data are also consistent with the response of dislocation lines to oscillating stress fields imposed on the solid. However, studies of solid helium in porous media, several control experiments, and the magnitude of the frequency shift found in this and other experiments all indicate that the most appropriate interpretation of the torsional oscillator results is the existence of a supersolid

The rock physics and geochemistry of carbonates exposed to reactive brines

^{4}\text{H}\text{e}

Pressure Effects Caused by CO2 Injection in the Snøhvit Field

phase.