A mechanism for Planckian metal phase in overdoped cuprate superconductors

The mysterious strange metallic state showing perfect T-linear resistivity and an associated universal scattering rate 1/τ = 2 π α k_b T/h with α ~1 a constant prefactor (h being Planck's constant) as well as logarithmic-in-temperature singular specific heat coefficient, so-called “Planckian metal state” was observed in various overdoped high-Tc cuprate superconductors [1]. The microscopic origin of these exotic behaviors remains elusive. Here, we offer a mechanism for this phenomenon based on quantum critical charge fluctuations within slave-boson approach to the two-dimensional t-J model. This model is further mapped onto an effective Kondo-Heisenberg-like model Hamiltonian. Via perturbative renormalization group analysis of the effective model, a quantum critical Planckian metal phase over a finite range in hole doping is realized near a localized-delocalized (Kondo breakdown) transition where bosonic charge (effective Kondo) fluctuations coupled to conduction band and gapless fermionic spinons [2]. The relevance of our results for overdoped high-Tc cuprate superconductors is discussed.