Doping dependence of the low-temperature planar carrier density in overdoped YBa 2 Cu 3 O 7 − δ

Whether a quantum critical point (QCP) demarcates the end of the pseudogap (PG) regime in hole-doped cuprates at a singular doping level {p}^*≈0.19 is still an open question. A crucial component of the puzzle is the manner in which the carrier density predicted by electronic structure calculations is recovered for p>{p}^* . Here, we use magnetic fields up to 67 T to suppress superconductivity down to 50 K, allowing us to simultaneously measure the low-temperature Hall number {n}_H and the in-plane resistivity anisotropy {ρ}_a/{ρ}_b in overdoped {Y}_1−x{Ca}_x{Ba}₂{Cu}₃{O}_7−δ single crystals. We confirm a previous finding [S. Badoux , ] that {n}_H (50 K) exhibits a sharp increase below {p}^* and use the measured resistivity anisotropy to obtain the planar carrier density {n}_pl={n}_H{({ρ}_a/{ρ}_b)}⁻¹ . The doping dependence of {n}_pl (50 K) reveals two key findings: (i) At optimal doping, {n}_pl≈p , and (ii) the sharp rise in {n}_H(p) is softened to such an extent that the full Fermi volume ( {n}_pl=1+p ) is only partially recovered at {p}^* . The latter result disfavors a conventional QCP scenario in which the PG end point leads to a reconstructed Fermi surface.