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Title: Is the Planckian scattering rate universal, and is it a bound
Plain: Data in several materials suggest the electron scattering rate equals temperature times a fixed combination of Boltzmann's and Planck's constants; it is unknown whether this is a true limit.
Precise: With $\hbar/\tau = \alpha k_B T$ extracted from the T-linear resistivity slope and the independently measured effective mass and carrier density, test whether $\alpha = 1$ within error across strange metals and whether any metal sustains $\alpha >> 1$. An answer is a proof of a bound on the transport scattering rate within a defined class of models, or a material with reliably measured $\alpha$ well above 1.
Settled by: Quantum-oscillation or specific-heat masses combined with resistivity slopes in many materials, plus a theorem bounding $\hbar/\tau$ in a stated class of models.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Analyses of several hole-doped cuprates (2019) gave $\alpha \sim 1$; no rigorous bound on the transport rate is known.
Posed since: 2004