The electrical conductivity of the Cu-P films was measured by current-voltage (I-V ) lines 4 using the van der Pauw (vdP) method and excitation currents of 100 µA (Cu 3-z P) and 1 µA (Cu 1.61 P and CuP 2-y ). The I-V characteristics show linear behavior (see Fig. )) for the shown data range in Fig. (a) of the main article. Some of the low-temperature data was discarded due to a noisy vdP correction factor in Cu 1.61 P and high contact resistances (> 1 × 10 8 Ω) in CuP 2-y , resulting in non-linear I-V characteristics.