Charge order near the antiferromagnetic quantum critical point in the trilayer high T_c cuprate HgBa₂Ca₂Cu₃O_(8+ δ)

We study the transport properties of underdoped trilayer cuprate HgBa$_2$Ca$_2$Cu$_3$O$_{8+ \delta}$ with doping level $p$ = 0.1 - 0.12 in magnetic field up to 88 T. We report for the first time in a cuprate superconductor a dramatic change of the quantum oscillation spectrum versus temperature, which is accompanied by a sign change of the Hall effect below $T \approx$ 10 K. Based on numerical simulations, we infer a Fermi surface reconstruction in the inner plane from an antiferromagnetic state (hole pockets) to a biaxial charge density wave state (electron pockets). We show that both orders compete and share the same hotspots of the Fermi surface and we discuss our result in the context of spin-fermion models.