Structure of Halo and Quasi-halo Helium–Helium–Alkali Trimers

Abstract

We report a diffusion Monte Carlo study of A 4 He 2 and A 4 He 3 He trimers' structural properties, were A is one of the alkali atoms 6,7 Li, 23 Na, 39 K, 85 Rb or 133 Cs. Some of them are in a pure halo state, characterized by large spatial extent and universality, while some are close to the halo limit. The theoretical analysis of these trimers enables insight on how structural properties of weakly bound systems change when approaching the halo edge. For that purpose, two-variable distributions of inter-particle separations and angles were calculated. Extreme spatial extensions of some trimers with 3 He confirm their halo nature. Although all the considered systems are floppy, trimers with all bound dimer subsystems are less spread and have significantly lower percentage of quasi-linear configurations than those which have at least one unbound dimer subsystem.

Ground-state characteristics of helium–alkali tetramers

“…It remains unknown what happens in the case of very small 4 He- 3 He clusters doped with an alkali atom. Those systems should be more diffuse than He A 4 3 in accordance with the manifestation of pure halo characteristics in He-A trimers with 3 He atoms [10,24,25], which are weak binding and large spatial extension.…”

“…Thus we expect He-A tetramers to form either a halo state or a somewhat less diffuse system. Weak binding and large spatial extension of He-A trimers have already been confirmed by numerous theoretical studies [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. However, among small He-A clusters which are larger than trimers only He Li were studied [18].…”

“…Quick ground-state equilibration was reached by adjusting reference energy E r during a simulation. A similar procedure was applied as in research of helium-alkali trimers [24,25]. The same masses were used and the potential was again constructed as the sum of the pair potentials.…”

“…The Hartree-Fock plus damped dispersion B-potential form (HFDB) [44] was used for He-He interactions, while He-A interactions were modeled by Kleinekathöfer, Tang, Toennies and Yiu potential form (KTTY) [45]. The same models were used in our previous research [10,24,25,46].…”

“…All clusters mentioned in this paragraph are very weakly bound under natural conditions. Thus, they have played a significant role in research of universality in halo dimers and trimers [8,10,25].…”