Figure 4: Hierarchy and interplay of underlying degrees of freedom.

In the formation of the 2DEG, quantum confinement reconstructs the bulk electronic structure into a rich array of intersecting orbitally ordered subband states. The interplay of this with spin–orbit coupling lifts the spin degeneracy of these bands, particularly strong around their crossings, through an orbitally enhanced Rashba-like interaction. Electron–phonon and electron–electron interactions further renormalise these spin–split dispersions, increasing the quasiparticle masses close to the Fermi level and causing a complete bandwidth narrowing of the shallow d_xz/yz states that pins the orbitally ordered band crossings close to the energy of the lowest phonon mode. This, in turn, sets the energy scale for enhanced spin–orbit splittings around these crossings, strongly entangling the charge, spin, orbital and lattice degrees of freedom of the 2DEG on a low-energy scale (orange shading).