Is the anomalous metal a true zero-temperature phase?
In plain words
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 statement
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.
What would settle it
Measurements with calibrated electron thermometry and progressively improved radiation filtering in several material classes, showing whether the saturation disappears or stays unchanged.
Status in the literature
Unverified 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.