Coherent electron Compton scattering and the non-diagonal electron momentum density of solids.

• Coherent Compton scattering is due to interference of the incident and Bragg beams. • It probes non-diagonal terms in the momentum density matrix for solid-state electrons. • The conditions for a directly interpretable coherent Compton EELS signal are derived. • Experimental results are presented for silicon under 004 and 2 ¯ 20 diffraction conditions. Experimental techniques that probe the electronic structure of crystalline solids are vital for exploring novel condensed matter phenomena. In coherent Compton scattering the Compton signal due to interference of an incident and Bragg diffracted beam is measured. This gives the projected, non-diagonal electron momentum density of the solid, a quantity that is sensitive to both the amplitude and phase of the electron wavefunction. Here coherent electron Compton scattering is demonstrated using electron energy loss spectroscopy in the transmission electron microscope. The technique has several advantages over coherent X-ray Compton scattering, such as a superior spatial resolution and the use of smaller specimens to generate Bragg beams of sufficient intensity. The conditions for a directly interpretable coherent electron Compton signal are established. Results are presented for the projected, non-diagonal electron momentum density for silicon under 004 and 2 ¯ 20 Bragg beam set ups. [ABSTRACT FROM AUTHOR]