Fermi-surface pockets in magnetic underdoped cuprates from first principles

Using an innovative first-principles band theory enabling the exploration of Mott-insulating magnetic cuprates, we study the Fermi surface of underdoped Y${}_{1-x}$Ca${}_x$Ba${}_2$Cu${}_3$O${}_6$ in a selection of magnetically ordered and polaronic states. All phases exhibit qualitatively similar, hole-like nodal-point small pockets. Their properties (area, masses, mass sign) only partially match those extracted from recent quantum-oscillation experiments. Ab initio calculations, therefore, do not straightforwardly support a magnetic origin of quantum oscillations.