Minimum Metallic Conductivity and Thermopower in Thin Palladium Films

The effects of two-dimensional electron localization have been studied by measuring thermopower and resistivity of thin (18-25 Å) films of palladium. "Metallic" samples have a small thermopower which tends to zero as $T\to 0$. Insulating samples have large thermopower which increases as $T\to 0$. The metal-insulator transition in Pd films thus involves the opening of a gap at the Fermi energy. With use of the thermopower to define the metal-insulator transition a critical resistivity of ∼ 30 kΩ/□ is found.