A formula for potential U of the He-4--He-4 interaction in the liquid state is obtained by the direct electromagnetic computation as a function of the interatomic distance R. The potential decreases exponentially at large R. The further development and application of the result are discussed.
The new interatomic potential g(r), providing the tunnelling of atoms, is suggested for calculating HFB phonon-roton spectrum E(p) of liquid He-4. The tunnelling enables the calculations to reproduce the experimental dependence of shifts E(p) on pres
sure P induced by He-3 admixture in the constant total density and volume.
We present precision neutron scattering measurements of the Bose-Einstein condensate fraction, n0(T), and the atomic momentum distribution, nstar(k), of liquid 4He at pressure p =24 bar. Both the temperature dependence of n0(T) and of the width of ns
tar(k) are determined. The n0(T) can be represented by n0(T) = n0(0)[1-(T/T{lambda}){gamma}] with a small n0(0) = 2.80pm0.20% and large {gamma} = 13pm2 for T < T{lambda} indicating strong interaction. The onset of BEC is accompanied by a significant narrowing of the nstar(k). The narrowing accounts for 65% of the drop in kinetic energy below T{lambda} and reveals an important coupling between BEC and k > 0 states. The experimental results are well reproduced by Path Integral Monte Carlo calculations.
We report results of diffusion Monte Carlo calculations for both $^4$He absorbed in a narrow single walled carbon nanotube (R = 3.42 AA) and strictly one dimensional $^4$He. Inside the tube, the binding energy of liquid $^4$He is approximately three
times larger than on planar graphite. At low linear densities, $^4$He in a nanotube is an experimental realization of a one-dimensional quantum fluid. However, when the density increases the structural and energetic properties of both systems differ. At high density, a quasi-continuous liquid-solid phase transition is observed in both cases.
A density functional theory is used to investigate the instability arising in superfluid $^4$He as it flows at velocity u just above the Landau critical velocity of rotons v_c. Confirming an early theoretical prediction by one of us [JETP Lett. 39, 5
11 (1984)], we find that a stationary periodic modulation of the density occurs, with amplitude proportional to (u-v_c)^{1/2} and wave vector equal to the roton wave vector. This density pattern is studied for supercritical flow both in bulk helium and in a channel of nanometer cross-section.
de Haas-van Alphen oscillation spectrum is studied for an idealized two-dimensional Fermi liquid with two parabolic bands in the case of canonical (fixed number of quasiparticles) and grand canonical (fixed chemical potential) ensembles. As already r
eported in the literature, oscillations of the chemical potential in magnetic field yield frequency combinations that are forbidden in the framework of the semiclassical theory. Exact analytical calculation of the Fourier components is derived at zero temperature and an asymptotic expansion is given for the high temperature and low magnetic field range. A good agreement is obtained between analytical formulae and numerical computations.