Correlation-Enhanced Effective Mass of Two-Dimensional Electrons in Mg_xZn_(1−x)O/ZnO Heterostructures

Abstract

We performed combined magnetotransport and cyclotron resonance experiments on two-dimensional electron systems confined in the Mg_xZn_(1−x)O/ZnO heterostructures over a wide range of carrier densities, from 1.9 to 12 × 10¹¹ cm⁻² (3.5 ≲ r_s ≲ 10, where r_s is the Wigner-Seitz radius). As the carrier density was reduced, the transport mass m*∗_(tr) was strongly enhanced. In marked contrast, the effective masses determined from the cyclotron resonance m^∗_(CR) were found to be independent of the carrier density and as large as the bulk effective mass. The large enhancement of m^∗_(tr), which exceeds m^∗_(CR) by ∼60%, at the lowest carrier density with r_s ∼ 10 is purely attributed to the strong electron correlation.

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