Effect of Twinning on Angle-Resolved Photoemission Spectroscopy Analysis of Ni_49.7Mn_29.1Ga_21.2(100) Heusler Alloy

We have solved a long-standing problem of missing intensity in the angle-resolved photoemission spectrum from the martensite phase of Heusler alloy Ni_49.7Mn_29.1Ga_21.2. In disagreement with ab initio calculations that predict a noticeable intensity in the central part of the Brillouin zone, the measured spectra show a negligible intensity. It casts a doubt on the validity both of theory and experiment. We have found that photoelectrons leaving the material are deflected by repeated scatterings on interfaces between the nanotwins present in the surface reagion, which prevents them to leave in direction perpendicular to the surface. This explains observed suppression of intensity in the centre of the Brillouin zone.