Incoherent transport and the evolution of power-law scaling of the magnetoresistance in cuprate superconductors.*

The normal state of overdoped cuprate superconductors within the strange metal regime (p* < p < p_sc) is characterized by a T-linear in-plane resistivity that persists to lowest temperatures and grows with the strength of superconductivity as optimal doping is approached from the overdoped end of the superconducting dome at p_sc until p* (the doping at which the pseudogap temperature reaches 0 K). Analysis of the high-field, low-temperature Hall coefficient reveals a simultaneous reduction in carrier density n_H from 1+p → p [1] indicating that coherent quasiparticles are being lost. We report high-field in-plane magnetoresistance (MR) studies of Tl2201 and Bi2201 in which signatures of incoherent transport are observed. In particular, an unexpectedly large linear-in-field MR has been observed at high H and low T that is insensitive to disorder, magnetic-field orientation and obeys quadrature (H/T) scaling [2]. The growth of the magnitude of the linear-in-H MR coincides with the growth of the low-T T-linear resistivity [3]. At p < p* ∼ 0.19, the growth of the linear-in-field MR at high fields persists, yet a dramatic change in the low-field behavior occurs. The quadrature (H/T) power-law scaling that is obeyed for p > p* abruptly cedes to H/T² scaling as the pseudogap regime is entered [3]. The anticorrelation of the loss of coherent quasiparticles probed via the Hall effect and the growth of the incoherent MR indicates the presence of two charge sectors. Such an anticorrelation naturally prompts the question: from which of these charge sectors does superconductivity emerge? We also present evidence to support the hypothesis that superconductivity emerges from those carriers that exhibit signatures of incoherent transport [4].