Experimental study of the Ioffe-Regel criterion for amorphous indium oxide films

The Ioffe-Regel criterion predicts the existence of a metal-insulator transition in a film series when the parameter k(F)l(e) satisfies the criterion k(F)l(e) approximate to 1; here k(F) is the Fermi wavenumber and l(e) is the elastic mean free path of the carriers. According to this criterion, films having k(F)l(e) >> 1 are metallic, while films having k(F)l(e) << 1 are insulating. We experimentally observe the metal-insulator transition in amorphous indium oxide films at k(F)l(e) = 5.2 +/- 0.5. The values of k(F)l(e) were calculated from room temperature resistivity and Hall voltage measurements, while the metal-insulator transition was determined from low-temperature resistivity data using the 'w'-criterion of Mobius and of Zabrodskii and Zinov'eva.