Quantum cavitation in liquid helium

Using a functional-integral approach, we have determined the temperature below which cavitation in liquid helium is driven by thermally assisted quantum tunneling. For both helium isotopes, we have obtained the crossover temperature in the whole range of allowed negative pressures. Our results are compatible with recent experimental results on 4He.

From nonwetting to prewetting: The asymptotic behavior of 4He drops on alkali substrates

We investigate the spreading of 4He droplets on alkali-metal surfaces at zero temperature, within the frame of finite range density-functional theory. The equilibrium configurations of several 4HeN clusters and their asymptotic trend with increasing particle number N, which can be traced to the wetting behavior of the quantum fluid, are examined for nanoscopic droplets. We discuss the size effects inferring that the asymptotic properties of large droplets correspond to those of the prewetting film.

Freezing of 4He and its liquid-solid interface from density functional theory

We show that, at high densities, fully variational solutions of solidlike types can be obtained from a density functional formalism originally designed for liquid 4He . Motivated by this finding, we propose an extension of the method that accurately describes the solid phase and the freezing transition of liquid 4He at zero temperature. The density profile of the interface between liquid and the (0001) surface of the 4He crystal is also investigated, and its surface energy evaluated. The interfacial tension is found to be in semiquantitative agreement with experiments and with other microscopic calculations. This opens the possibility to use unbiased density functional (DF) methods to study highly nonhomogeneous systems, like 4He interacting with strongly attractive impurities and/or substrates, or the nucleation of the solid phase in the metastable liquid.

Condensation of helium in nanoscopic alkali wedges at zero temperature

We present a complete calculation of the structure of liquid 4He confined to a concave nanoscopic wedge, as a function of the opening angle of the walls. This is achieved within a finite-range density functional formalism. The results here presented, restricted to alkali metal substrates, illustrate the change in meniscus shape from rather broad to narrow wedges on weak and strong alkali adsorbers, and we relate this change to the wetting behavior of helium on the corresponding planar substrate. As the wedge angle is varied, we find a sequence of stable states that, in the case of cesium, undergo one filling and one emptying transition at large and small openings, respectively. A computationally unambiguous criterion to determine the contact angle of 4He on cesium is also proposed.

Deformed-jellium model for the fission of multiply charged metal clusters

A deformed-jellium model is used to calculate the fission barrier height of positive doubly charged sodium clusters within an extended Thomas-Fermi approximation. The fissioning cluster is continuously deformed from the parent configuration until it splits into two fragments. Although the shape of the fission barrier obviously depends on the parametrization of the fission path, we have found that remarkably, the maximum of the barrier corresponds to a configuration in which the emerging fragments are already formed and rather well apart. The implication of this finding in the calculation of critical numbers for fission is illustrated in the case of multiply charged Na clusters.

Cavitation in 3He-4He liquid mixtures at low temperatures

Bubble formation in solutions of 3He and 4He is studied within a density-functional approach. In particular, the temperature dependence of the cavitation pressure for different 3He concentrations is calculated at low temperatures and compared to that of pure 4He. The presence of Andreev states lowers the surface tension and, consequently, nucleation barriers are drastically reduced. This fact means that even at low 3He concentrations the cavitation process takes place at higher pressures than the spinodal pressure, which is not the case for pure 4He.