Wave-packet propagation study of the charge-transfer dynamics of Rydberg atoms with metal surfaces

Abstract

A wave-packet propagation study is presented of the ionization dynamics of xenon and hydrogen Rydberg atoms interacting with a metal surface in the presence of an external field. The calculations are performed using a Coulomb-wave discrete variable representation, which allows an efficient extension of previous calculations to a higher principal quantum number. The wave-packet calculations include nonadiabatic effects at avoided energy level crossings. Ionization probabilities as a function of distance from the surface are compared with complex-scaling calculations, which assume purely adiabatic traversal of the avoided crossings. A comparison is made between the dynamics calculated for the "normal" experimental situation, where the applied field is oriented so as to repel positive ions away from the surface, versus the dynamics for the reversed field situation, in which electrons are repelled from the surface. Overall it is clear that reversing the field direction has a pronounced effect on the ionization dynamics for any given starting level and that the nonadiabatic effects are most pronounced in the reversed field case. For certain field ranges, electron flux is found to be "backscattered" away from the surface in the reversed field configuration. Preliminary mean-field calculations are also presented to evaluate the effect of the acceleration of the atom on the ionization dynamics.

Interaction of Rydberg atoms with surfaces

“…However, the surface-perturbed energy levels within a n manifold can undergo many level crossings as the surface is approached. This has been shown by So et al by calculating energy levels of a Rydberg state in front of a surface using a complex scaling method [35], where the crossings are attributed to breaking of parity in the z direction. Complex scaling is a coordinate transformation method used as a tool to study resonance and ionisation processes for weakly bound states.…”

“…The parameters for the Jellium model are selected for aluminium. The figure is adapted with permission from reference [35], copyrighted by the American Physical Society.…”

“…where the attractive V pp term is cancelled by a repulsive term from the expansion but could otherwise be motivated to be omitted because it raises the energy of both the Rydberg state and the energy states of the surface equally and therefore does not affect the surface ionisation dynamics [35]. The total potential would additionally contain the Coulomb potential, V tot = V surface + V Coulomb , where V Coulomb = −1/r and the distance r is the separation between ion core and electron.…”

“…The surface sits at a position of −30 a 0 relative to the center of the electronic potential at z = 0. Note that this reference system is chosen in various calculations discussed in the text as performed by So et al [35]. Here, the symmetry center of the atom is selected to lie statically at z = 0 and the surface is moved towards the atom.…”

“…In the following, the focus will be on the interplay of an highly excited atomic state with a metallic surface, particularly the process of ionisation, which has been a subject of several investigations over the last three decades in experimental studies [27][28][29][30][31] as well as in theoretical studies [32][33][34][35]. In Sect.…”