Reduced Hall carrier density in the overdoped strange metal regime of cuprate superconductors

Efforts to understand the microscopic origin of superconductivity in the cuprates are dependent on knowledge of the normal state. The Hall number in the low-temperature, high-field limit n_H(0) has a particular importance because, within conventional transport theory, it is simply related to the number of charge carriers, so its evolution with doping gives crucial information about the nature of the charge transport. Here we report a study of the high-field Hall coefficient of the single-layer cuprates Tl₂Ba₂CuO_6+δ (Tl2201) and (Pb/La)-doped Bi₂Sr₂CuO_6+δ (Bi2201), which shows how n_H(0) evolves in the overdoped—so-called strange metal—regime of cuprates. We find that n_H(0) increases smoothly from p to 1 + p, where p is the number of holes doped into the parent insulating state, over a wide range of doping. The evolution of _nH correlates with the emergence of the anomalous linear-in-temperature term in the low-temperature in-plane resistivity. The results could suggest that quasiparticle decoherence extends to dopings well beyond the pseudogap regime.