The role of defects in Supersolid Helium-4 (original) (raw)

Quantum plasticity and supersolid response in helium-4

Physical Review B, 2014

We argue that the three key phenomena recently observed in solid 4 He-mass supertransport, anomalous isochoric compressibility (syringe effect), and giant plasticity-are closely linked to each other through the physics of an interconnected network of tilted quantum-rough dislocations. As immediate implications of this connection several predictions follow: In the absence of 3 He impurities, the syringe effect and giant plasticity persist down to T = 0; the dynamical low-frequency syringe and giant-plasticity responses are dispersionless; and similarly to giant plasticity but without direct relationship to the supertransport along the dislocation cores, 3 He impurities should suppress the syringe effect partially or completely at appropriately low temperatures.

Solid 4 He 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

Journal of The Physical Society of Japan, 2008

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.

Evidence for a Superglass State in Solid 4 He

Science, 2009

Glasslike Supersolid Recent experiments with solid helium confined to the ring of a torsional oscillator at extremely low temperatures have been interpreted in terms of an exotic supersolid phase—a crystalline solid that somehow flows like a superfluid. However, behavioral differences between samples have raised many questions (see the Perspective by Saunders ). Hunt et al. (p. 632 ) present a comprehensive study of the relaxation dynamics of the torsional oscillator system as a function of time and temperature. The data provides evidence for a “supersolid glass,” where glassy behavior of crystal dislocations and superfluidity can coexist. In a separate theoretical study, Anderson (p. 631 ) argues that supersolidity ought to be a ground state for all bose solids, but that defects in the sample may mask the supersolid signature.

Local Stress and Superfluid Properties of Solid He4

Physical Review Letters, 2008

More than half a century ago Penrose asked : are the superfluid and solid state of matter mutually exclusive or do there exist "supersolid" materials where the atoms form a regular lattice and simultaneously flow without friction? Recent experiments provide evidence that supersolid behavior indeed exists in 4 He -the most quantum material known in Nature. In this paper we show that large local strain in the vicinity of crystalline defects is the origin of supersolidity in 4 He. Although ideal crystals of 4 He are not supersolid, the gap for vacancy creation closes when applying a moderate stress. While a homogeneous system simply becomes unstable at this point, the stressed core of crystalline defects (dislocations and grain boundaries) undergoes a radical transformation and can become superfluid.

A Classical Picture of the Role of Vacancies and Interstitials in Helium-4

Journal of Low Temperature Physics, 2008

Motivated by experimental hints for supersolidity in Helium-4, we perform Monte Carlo simulations of vacancies and interstitials in a classical two-and three-dimensional Lennard-Jones solid. We confirm a strong binding energy of vacancies which is of the order of Lennard-Jones attraction. This is reminiscent of what has been found for vacancies in Quantum Monte Carlo simulations. In addition, we find a strong attraction and large binding energy of interstitials in two-dimensional simulations. This is mainly due to the formation of a pair of dislocations by clustering interstitials, in which minimizes the elastic deformation energy. We interpret the results in light of the properties of Helium-4.

Observation of superfluid components in solid ^4He

Neutron scattering demonstrated that localized superfluid components exist at high pressure within solid helium in aerogel [1]. Two sharp phonon-roton spectra are clearly distinguishable from modes in bulk superfluid helium. These roton excitations exhibit different roton gap parameters than the roton observed in the bulk fluid at freezing pressure. One of the roton modes disappears after annealing. Comparison with theoretical calculations suggests that the model that reproduces the observed data best is that of superfluid double layers within the solid and at the helium-substrate interface. The elastic scattering evidenced in addition to the hcp phase also the bcc-phase. both consisting of a small crystallites as a consequence of the confinement. The structural aspect of coexisting hcp and bcc phases in the aerogel matrix seems to be important for the creation of the localized superfluid components.[4pt] [1] H. Lauter, E. Krotscheck, E. Kats, A. V. Puchkov, V. V. Lauter, V. Apaja, ...

Symmetry breaking phenomena in liquid Helium-4

1988

Salient features of liquid Helium II are being analysed In the light of symmetry breaking wechanisn. The excitation spectrum 1* derived by scaling transformation. A relation between roton excitation and Bogoliubov's quasi particles has been established by giving different structures to the roton operators,similar to quasi boson approximation for phonon-like spectrum. This structure of the roton operators enables us to study the low temperature behaviour of superfluid He Hum-4 by introducing the idea of pairing for roton-like excitation for the on set of energy-gap. Superflutd He^ is divided into the states of condensed bosons, oscillating condensed bosons, phonons, maxons, rotons and the states of vortices. We consider the transition probabilities between these various states. Coherent states of various superfluid regions of He II are being obtained and consistently analysed which have deep inter-relatlonshlp. As higher excitations have also a group structure and their coherent behaviour has been seen, this formalism seems to be more appropriate to deal with such an interesting problem. HIRAHARE-TRIESTE

Supersolid He4 likely has nearly isotropic superflow

Physical Review B, 2006

We extend previous calculations of the zero temperature superfluid fraction f s (SFF) vs localization, from the fcc lattice to the experimentally realized (for solid 4 He) hcp and bcc lattices.