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 N(c) has been measured at very low temperatures (0.04 less-than-or-equal-to T less-than-or-equal-to 3 K). For N >> N(c), S is negative and shows the linear T dependence of a metal, whereas close to N(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,