Electrical properties of isotopically enriched neutron-transmutation-doped Ge-70 : Ga near the metal-insulator transition

摘要

We report low-temperature carrier transport properties of a series of nominally uncompensated neutron-transmutation-doped Ce-70:Ga samples very close to the critical concentration N-c for the metal-insulator transition. The nine samples closest to N-c have Ga concentrations N in the range 0.99N(c)N-c. The values of T-0 agree very well with theoretical estimates based on the modified Efros and Shklovskii relation k(B)T(0)approximate to(2.8e(2)/4 pi epsilon(0)kappa(0)xi(0))(1 - N/N-c)(alpha), where kappa(0) and xi(0) are the dielectric constant and the Bohr radius, respectively. The insulating samples very close to the transition (0.991N(c)