LOGARITHMIC TEMPERATURE-DEPENDENCE OF THE CONDUCTIVITY OF THE 2-DIMENSIONAL METAL

We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity, which causes t he conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease g radually with density, to vanish at a critical density n(c,2)similar t o 2 X 10(12) cm(-2) , and then to have the opposite sign at n > n(c,2) . The second critical density sets the upper limit on the existence re gion of the 2D metal, whereas the conductivity at the critical point, Gc, 2 similar to 120 e(2)/h, sets an upper (low-temperature) limit on its conductivity. (C) 1998 American Institute of Physics. [S0021-3640( 98)01218-3]