Spin and orbital momentum of electrons : a new era in electron microscopy

Date: 
Monday, April 6, 2015 -
4:00pm to 5:00pm
Speaker: 
Vincenzo Grillo
Speaker's Institution: 
CNR-Istituto Nanoscienze, in Modena, Italy

1. Department of Physics, University of Oregon, Eugene, 97403-1274 Oregon, USA

2. CNR-Istituto Nanoscienze, Centro S3, Via G. Campi 213/a, I-41125 Modena, Italy

3. CNR-IMEM Parco Area delle Scienze 37/A, I-43124 Parma, Italy

The introduction of electron vortex beam has been the beginning of a completely new way to see at electron microscopy. It not only has disclosed the use of Orbital Angular Momentum  degree of freedom previously neglected but has also started the idea that we can generate arbitrary wavefunctions  for innovative experiments.

After highlighting some of my experimental contributions to the generation and characterization different vortex states I’ll concentrate on one fascinating application of Vortex beams: the possibility of OAM-spin conversion and therefore to produce a spin filter to polarize electrons.

In fact while neutral atoms can be spin-filtered with the well-known “Stern Gerlach” experiment, no experiment has so far succeeded to prove a significant spin polarization on e-beam based on microscopic fields, in fact the only known methods are based on interaction with materials (e.g Mott scattering)  

The problem has been already affronted by Bohr who conjectured a sort of “interdiction principle” for such polarization experiments. We proposed the use of vortex beam to circumvent the problem , but subtle effects have to be taken into account. I’ll go through a discussion  of such effects and propose experimental configurations that will require “ad-hoc” electro-optical configurations.