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Title: Is the anomalous metal a true zero-temperature phase?
Plain: Some thin superconducting films stop losing resistance on cooling and level off at a small value. The dispute is whether this is a genuine state of matter or a result of electrical noise and stray radiation that keep the electrons warmer than the thermometer.
Precise: In $2\mathrm{D}$ superconducting films and arrays (amorphous InOx, MoGe, Ta, transition-metal dichalcogenide superconductors, Josephson-junction arrays) tuned by $B$, gate or disorder near the superconductor-insulator transition, $\rho(T)$ saturates below $T \sim 0.1\,T_c$ at $1e-3\ \text{to}\ 1e-1$ of the normal-state value. Determine whether the saturation survives when electron temperature and external radiation are independently controlled (filtered leads, shielding, noise thermometry), i.e. whether $\rho(T \to 0) > 0$ holds in a finite parameter range.
Settled by: Measurements with calibrated electron thermometry and progressively improved radiation filtering in several material classes, showing whether the saturation disappears or stays unchanged.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Radiation filtering removed the saturation in amorphous InOx and 2H-NbSe2 (Tamir et al., Science Advances 5, eaau3826, 2019), while other groups report saturation that persists with filtering in other films; no consensus as of 2026.
Posed since: (empty)