Theory of universal Planckian metal near local criticality

The mysterious metallic phase showing universal linear-in-temperature scattering rate with quantum critical scaling and logarithmic-in-temperature singular specific heat coefficient, so-called “Planckian metal phase”, has been observed in various high-Tc cuprate superconductors near optimal doping. Recently, the unconventional features of this exotic phase have been well accounted for within a heavy-fermion reformulated slave-boson t-J model [1]. Here, we show that this effective model is exactly solvable in the large-N multi-channel (K screening channels) limit [2]. The non-superconducting ground state supports a universal quantum critical Planckian metal phase, made of disordered local bosonic charge fluctuations coupled to both spinon and a heavy conduction-electron Fermi surfaces near a Kondo breakdown-like local quantum critical point. Furthermore, this state shows a bad metallic transport property with perfect T-linear resistivity persisting beyond the Mott-Ioffe-Regel quasi-particle limit, in good agreement with the experimental observations on cuprates.