Magnetoresistance and Symmetry of a Two-Dimensional Electron Gas in AlGaN/AlN/GaN Heterostructures

The physical characteristics of a two-dimensional electron gas located in the GaN layer near the AlN/GaN interface of AlGaN/AlN/GaN heterostructures have been studied for decades. According to the currently accepted concepts, its symmetry coincides with that of the nonsymmorphic space group C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{{6{v}}}<^>{4}$$\end{document} in the bulk of GaN. However, this is incorrect. Indeed, the only nonsymmorphic element of this group-the rotation of the system about the [0001] axis normal to the interface plane, with a simultaneous shift along this axis by half a period of the GaN crystal lattice-is forbidden for a two-dimensional gas owing to the confinement potential, which, therefore, reduces its symmetry to the symmetry of the trigonal point group C \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_{{3{v}}}$$\end{document} . This fact has been confirmed in this work by ab initio density functional calculations and by electrophysical data.