Signals of strong electronic correlation in ion scattering processes

Abstract

Previous measurements of neutral atom fractions for Sr + scattered by gold polycrystalline surfaces show a singular dependence with the target temperature. There is still not a theoretical model that can properly describe the magnitude and the temperature dependence of the neutralization probabilities found. Here, we applied a first-principles quantum-mechanical theoretical formalism to describe the time-dependent scattering process. Three different electronic correlation approaches consistent with the system analyzed are used: (i) the spinless approach, where two charge channels are considered (Sr 0 and Sr + ) and the spin degeneration is neglected; (ii) the infinite-U approach, with the same charge channels (Sr 0 and Sr + ) but considering the spin degeneration; and (iii) the finite-U approach, where the first ionization and second ionization energy levels are considered very, but finitely, separated. Neutral fraction magnitudes and temperature dependence are better described by the finite-U approach, indicating that e-correlation plays a significant role in charge-transfer processes. However, none of them is able to explain the nonmonotonous temperature dependence experimentally obtained. Here, we suggest that small changes in the surface work function introduced by the target heating, and possibly not detected by experimental standard methods, could be responsible for that singular behavior. Additionally, we apply the same theoretical model using the infinite-U approximation for the Mg-Au system, obtaining an excellent description of the experimental neutral fractions measured.

Charge Transfer in Low-Energy Collisions of Protons with a Thick C60 Film

“…Electron capture and loss processes during projectile–surface collisions involve complex mechanisms properly described by nonequilibrium quantum mechanics formalisms. − The variation of the incoming energy of the projectile as well as the incoming/exit collisional angle allows for probing charge exchange for different projectile–surface interaction times and a wide range of projectile velocity components parallel to the surface. ,− The typical time scale of the charge-exchange processes leads to collisional experiments ranging in the low- or very-low-energy regime (0.5–10 keV).…”

Surface states influence in the conductance spectra of Co adsorbed on Cu(111)

“…We consider the infinite-U approximation in a strong Hund's rule coupling regime, in which the configuration space is restricted to states with total spin S and S − 1 2 [1]. The infinite-U approach has been used for the description of atom-surface interacting systems in out-of-equilibrium dynamical and stationary situations [33,34,[37][38][39][40][41][44][45][46][47]. In particular, in Ref.…”

“…The Green functions are calculated by using the equations of motion method (EOM) [35,36] and closing the system of equations that involve an increasing number of particles in a second order in the atom-band coupling term [34]. The resolution method has been extensively discussed in different applications of this approach [33,34,[37][38][39][40][41], and therefore we present the derivation and final expressions in Appendix A.…”

“…We solve the ionic Hamiltonian by means of Green functions calculated using the equation of motion (EOM) method, closing the system of equations in a second order in the atom-band coupling term [34][35][36]. This method has been used in several systems where many-body effects become relevant [33,34,[37][38][39][40][41]. The introduction of the Hamiltonian and its solution are presented in Section II.…”

Multiorbital electronic correlation effects of Co adatoms on graphene: An ionic Hamiltonian approach

“…The EOM method requires a suitable decoupling scheme to close the chain of equations of successive Green functions, which involve an increasing number of particles. In this work the EOM are closed in a second order in V kd i , which has been proven to be successful for a qualitative description of the Kondo physics in many atom-surface interacting systems [32,[38][39][40]49]. Due to the degeneracy on the total spin projection M, the Green functions become independent of M and σ , so that we introduce G pq ≡ G Mσ pq and F pq ≡ F Mσ pq .…”