Controlling electron projectile coherence effects using twisted electrons

Abstract

In traditional scattering theory, the incident projectile is assumed to have an infinite coherence length. However, over the last decade, experimental and theoretical studies of collisions using heavy ion projectiles have shown that this assumption is not always valid. This has led to a growing number of studies that specifically examined the effects of the projectile's coherence length on collision cross sections. These studies have used heavy ion projectiles because they offer a straight-forward method to control the projectile's coherence length through its momentum, and using these techniques, it has been demonstrated that the projectile's coherence length alters the cross sections. In contrast, it is widely presumed that the coherence length of an electron projectile is always sufficiently large that any effects on the cross sections can be safely neglected. We show that, contrary to this prevailing opinion, coherence effects are observable for electron projectiles and they can be controlled. We calculate triple differential cross sections (TDCSs) for ionization of H2+ using twisted electron projectiles in the form of Laguerre-Gauss and Bessel electrons. Effects of the projectile's coherence length are observed through the presence or absence of two-slit interference features in the TDCSs. When the electron projectile's coherence length is large, ionization occurs from either nuclear center of the molecule, and two-slit interference features are visible in the TDCSs. In contrast, when the projectile's coherence length is small, ionization occurs from only one nuclear center and the TDCSs resemble those for ionization of atomic hydrogen. We demonstrate that the intrinsic parameters of the vortex projectiles, such as beam waist and opening angle, can be used to control the coherence length of electron projectiles.