We study the transport properties of underdoped trilayer cuprate
HgBa2βCa2βCu3βO8+Ξ΄β 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 Tβ 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.Comment: Main + Supplemental Informatio