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–

Abstract

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, U.S.A.) reported evidence for nonclassical rotational inertia effects, a typical signature of superfluidity, in samples of solid 4 He. 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 3 He 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 4 He with a strong resemblance to the phenomena revealed by torsional oscillator experiments. Very recently, the observation of unusual mass transport in hcp solid 4 He has also been reported, suggesting superflow. From the theoretical point of view, powerful simulation methods have been used to study solid 4 He, 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.

The geyser effect in the vacuum expansion of solid3He0.544He0.46and the determination of the Poisson ratio

“…In recent years, much experimental and theoretical effort has been devoted to understanding the low-temperature physical nature of solid pure 4 He, largely stimulated by the claimed observation of superfluidity [1]. The most recent consensus view indicates that the anomalies observed in the non-classical rotational inertia, shear modulus and the specific heat are not due to superfluidity of the ideal commensurate solid, but rather they must be related to vacancies and other intrinsic defects such as grain boundaries or dislocations, or extrinsic factors such as the 3 He impurity level [2]. Defects of a similar nature have been invoked to explain a phenomenon called the geyser effect, observed in the expansion of solid 4 He through a small orifice into vacuum under constant source pressure (P 0 ) and temperature (T 0 ).…”

Simultaneous measurement of torsional oscillations and NMR of very diluteH3ein solidH4Toda1, Gumann2, Kosaka3 et al. 2010Phys. Rev. B23210View full textAdd to dashboardCite

“…5 This experimental result attracted considerable interest and served as a starting point for many theoretical and experimental works. 7 Thus far, considerable information about the phenomenon of supersolidity has been obtained. The observed NCRIf decreases with an increase in the driving velocity.…”

Josephson effects in one-dimensional supersolids

“…The values of ϕ (±L/2) at the boundaries are determined by A(x) and J through (11). This setup describes a system attached to a current generator (one can regard this onedimensional system as an orifice attaching two reservoirs of superfluids or supersolids; see, e.g., Sec.…”

“…Although the possibility of supersolids was discussed theoretically about 40 years ago, 1-3 extensive and intensive studies started since Kim and Chan reported [4][5][6][7] the first evidence for nonclassical rotational inertia 3 in a solid phase of 4 He in torsional oscillator experiments. Subsequently, experimental studies have revealed various puzzling properties of supersolid 4 He: [8][9][10][11] the enhancement of elasticity having the same temperature dependence as the resonance frequency shift, 12 the sensitivity of the resonance frequency shift to the history of the annealing process 13 and to small concentrations of 3 He, 12 superflow along the grain boundaries, 14 and ultraslow relaxation dynamics in the dissipation and resonance frequency shift in the torsional oscillator experiments. 15 As a consistent explanation of these experimental results, several theories have been proposed, such as defectmediated superfluidity mechanisms, 16,17 a nonsuperfluid glass picture, 18,19 and intrinsic supersolidity of the defect-free crystal.…”