Thermoelectric power of a disordered metal near the metal-insulator transition

The thermoelectric power S of uncompensated Si:P with P concentration N near the metal-insulator transition occurring at Nc has been measured at very low temperatures (0.04{≤}T{≤}3 K). For N{}Nc, S is negative and shows the linear T dependence of a metal, whereas close to Nc an anomalous behavior with a sign change of S at low T is observed. The strong dependence of S on magnetic fields up to 6 T relates the anomaly to magnetic scattering, thus giving the first experimental evidence for localized moments near the metal-insulator transition in a transport property.