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 ${\mathit{N}}_{\mathit{c}}$ has been measured at very low temperatures (0.04≤T≤3 K). For N≫${\mathit{N}}_{\mathit{c}}$, S is negative and shows the linear T dependence of a metal, whereas close to ${\mathit{N}}_{\mathit{c}}$ 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.