A counterexample to the conjectured Planckian bound on transport

TL;DR

This paper presents a clear counterexample in overdoped electron-doped cuprates that challenges the recently proposed universal Planckian bound on transport relaxation rates in metals.

Contribution

It demonstrates that the transport relaxation rate in certain cuprates exceeds the supposed Planckian limit, questioning the universality of this bound.

Findings

Overdoped electron-doped cuprates violate the Planckian bound

Transport relaxation rate surpasses temperature in these materials

Challenges the universality of the Planckian limit in metals

Abstract

It has recently been conjectured that the transport relaxation rate in metals is bounded above by the temperature of the system. In this work, we discuss the transport phenomenology of overdoped electron-doped cuprates, which we show constitute an unambiguous counterexample to this putative "Planckian" bound, raising serious questions about the efficacy of the bound.