Metal-insulator transition induced by the magnetic field in n-type GaSb

The metal-insulator (MI) transition induced by a magnetic field was evidenced for the first time in compensated n-type GaSb layers grown by molecular beam epitaxy. The free electron densities were in the low 10¹⁶ cm⁻³ range or even slightly lower, so that the zero-field 3D electron gas was degenerate and, at the B_MI magnetic field of the MI transition, it populates only the spin-split 0⁽⁺⁾ Landau level (extreme quantum limit). On the metallic side of the MI transition a T^1/3 dependence of the conductivity was assumed to fit the low-T data and to estimate the B_MI value, which resulted of 9.1 T in the purest sample. The MI transition manifests in a strong increase of the diagonal resistivity with the magnetic field, but not of the Hall coefficient, suggesting that the apparent electron density is practically constant, whereas the mobility varies strongly. The evidence of a maximum in the temperature dependence of the Hall coefficient has been explained through a two channels transport mechanism involving localized and extended states.