Fermi-surface reconstruction in a weak square potential
= Fermi-surface reconstruction in a weak square potential
For a free circle of radius $R$ and square reciprocal period $Q$ with $\sqrt2R<Q<2R$, the circle cuts the faces but not the corners of the first zone. Weak Bragg gaps reconnect the folded branches into two inequivalent edge-centred <electron pockets> and one corner-centred <hole pocket>. The zero-potential limit retains band crossings instead of avoided crossings.