Planckian dissipation and scale invariance in a quantum-critical disordered pnictide

Quantum-mechanical fluctuations between competing phases at $T=0$ induce exotic finite-temperature collective excitations that are not described by the standard Landau Fermi liquid framework. These excitations exhibit anomalous temperature dependences, or non-Fermi liquid behavior, in the transport and thermodynamic properties in the vicinity of a quantum critical point, and are often intimately linked to the appearance of unconventional Cooper pairing as observed in strongly correlated systems including the high-$T_c$ cuprate and iron pnictide superconductors. The presence of superconductivity, however, precludes direct access to the quantum critical point, and makes it difficult to assess the role of quantum-critical fluctuations in shaping anomalous finite-temperature physical properties, such as Planckian dissipation $\hbar/\tau_{p} =k_{B}T$. Here we report temperature-field scale invariance of non-Fermi liquid thermodynamic, transport and Hall quantities in a non-superconducting iron-pnictide, Ba(Fe$_{1/3}$Co$_{1/3}$Ni$_{1/3}$)$_{2}$As$_{2}$, indicative of quantum criticality at zero temperature and zero applied magnetic field. Beyond a linear in temperature resistivity, the hallmark signature of strong quasiparticle scattering, we find a more universal Planck-limited scattering rate that obeys a scaling relation between temperature and applied magnetic fields down to the lowest energy scales. Together with the emergence of hole-like carriers close to the zero-temperature and zero-field limit, the scale invariance, isotropic field response and lack of applied pressure sensitivity point to the realization of a novel quantum fluid predicted by the holographic correspondence and born out of a unique quantum critical system that does not drive a pairing instability.