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Title: Origin of linear-in-temperature resistivity near the magic angle
Plain: Near the magic angle the electrical resistance grows in direct proportion to temperature over a wide range, a strange-metal behaviour also seen in cuprates, and its cause is unknown.
Precise: In twisted bilayer graphene near $\theta \sim 1.1\,\mathrm{deg}$, $\rho(T) \sim A T$ from $\sim 1\,\mathrm{K}$ to tens of K, with slope $A$ growing on approach to the magic angle and, at some fillings, a scattering rate near the Planckian value $\hbar/\tau \sim k_B T$. Determine whether this comes from electron-acoustic-phonon scattering enhanced by flat-band velocity renormalization or from electronic quantum criticality. An answer predicts $A(\theta, \nu)$ and the low-temperature cutoff quantitatively.
Settled by: Measurement of $A$ versus $\theta$ and $\nu$ compared with a parameter-free phonon calculation, plus tests in which phonons are altered or electronic fluctuations suppressed.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: contested
Status note: Phonon-based (2019) and Planckian electronic (2020-2022) interpretations both remain in use as of 2026.
Posed since: 2019