The scaled-invariant Planckian metal and quantum criticality in Ce$_{1-x}$Nd$_x$CoIn$_5$

TL;DR

This paper reports the observation of quantum-critical $T/B$-scaling of the Planckian metal state in Ce$_{1-x}$Nd$_x$CoIn$_5$, providing a microscopic mechanism linked to Kondo breakdown that explains universal scattering and critical thermodynamic behavior.

Contribution

It introduces the first microscopic mechanism based on critical charge fluctuations near Kondo breakdown to explain the Planckian state in quantum critical superconductors.

Findings

Observation of $T/B$-scaling in resistivity and heat capacity.

Identification of critical Kondo hybridization at $x_c \\sim 0.03$.

A microscopic model capturing universal Planckian scattering and quantum-critical scaling.

Abstract

Perfect $T$-linear resistivity associated with universal scattering rate: $1/\tau =\alpha k_B T/\hbar$ with $\alpha \sim 1$, so-called Planckian metal state, has been observed in the normal state of a variety of strongly correlated superconductors close to a quantum critical point. However, the microscopic origin of this intriguing phenomena and its link to quantum criticality still remains an outstanding open problem. In this work, we observe the quantum-critical $T/B$-scaling of the Planckian metal state in the resistivity and heat capacity of heavy-electron superconductor Ce$_{1-x}$Nd$_x$CoIn$_5$ in magnetic fields near the edge of antiferromagnetism, driven by critical Kondo hybridization at the critical doping $x_c \sim 0.03$. We further provide the first microscopic mechanism to account for the Planckian state in a quantum critical system based on the critical charge fluctuations near Kondo breakdown transition at $x_c$ within the quasi-two-dimensional Kondo-Heisenberg lattice model. This mechanism simultaneously captures the observed universal Planckian scattering rate as well as the quantum-critical scaling and power-law divergence in thermodynamic observables near criticality. Our mechanism is generic to Planckian metal states in a variety of quantum critical superconductors near Kondo destruction.