8 research outputs found
Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research
The possibility of a supersolid state of matter, i.e., a crystalline solid
exhibiting superfluid properties, first appeared in theoretical studies about
forty years ago. After a long period of little interest due to the lack of
experimental evidence, it has attracted strong experimental and theoretical
attention in the last few years since Kim and Chan (Penn State, USA) reported
evidence for nonclassical rotational inertia effects, a typical signature of
superfluidity, in samples of solid 4He. Since this "first observation", other
experimental groups have observed such effects in the response to the rotation
of samples of crystalline helium, and it has become clear that the response of
the solid is extremely sensitive to growth conditions, annealing processes, and
3He impurities. A peak in the specific heat in the same range of temperatures
has been reported as well as anomalies in the elastic behaviour of solid 4He
with a strong resemblance to the phenomena revealed by torsional oscillator
experiments. Very recently, the observation of unusual mass transport in hcp
solid 4He has also been reported, suggesting superflow. From the theoretical
point of view, powerful simulation methods have been used to study solid 4He,
but the interpretation of the data is still rather difficult; dealing with the
question of supersolidity means that one has to face not only the problem of
the coexistence of quantum coherence phenomena and crystalline order, exploring
the realm of spontaneous symmetry breaking and quantum field theory, but also
the problem of the role of disorder, i.e., how defects, such as vacancies,
impurities, dislocations, and grain boundaries, participate in the phase
transition mechanism.Comment: Published on J. Phys. Soc. Jpn., Vol.77, No.11, p.11101
Solid 4He : search for superfluidity
Theoreticians agree that superfluidity can exist in a Bose solid. The experiments to detect such an effect have failed up to now. We present here an argument that justifies the exploration of the 1 mK-20 mK temperature range. We have carried out an experiment to detect a mass flow through the solid 4 He down to 4 mK. No anomalous effect occurred, and this result therefore further reduces the upper limit for the occurrence of superfluidity in solid 4He to below 4 mK.L'existence d'une superfluidité pour un solide de bosons a été proposée par plusieurs théoriciens. Aucune expérience ne l'a jusqu'à présent révélée. Nous présentons un argument qui nous a incités à explorer la gamme de température 1 mK-20 mK. Nous avons tenté de détecter un courant de masse à travers du 4He solide à 4 mK. L'absence d'effet abaisse encore la borne supérieure pour la température de superfluidité de ce solide