Extreme field-induced cyclotron mass variations in coupled double quantum wells

Abstract

We observe deviations in the cyclotron effective mass m c near the partial energy gap formed in strongly coupled GaAs double quantum wells (QWs) subject to in-plane magnetic fields B ⊥. In k-space, B ⊥ shifts the two QW dispersion curves relative to one another, resulting in an anticrossing and opening the energy gap. This gives rise to large B ⊥-tunable distortions in the Fermi surface and density of states. This system is thus unique in that the Fermi surface and energy position of the gap can be controlled by sweeping B ⊥. Recently, Lyo has predicted that m c undergoes large variations as the partial energy gap is moved through the Fermi level by B ⊥. By tilting our sample by a small angle θ, we introduce a small perpendicular magnetic field B ⊥, in addition to B ⊥, and analyze the temperature dependence of the resulting Shubnikov-de Haas oscillations to obtain m c( B ⊥). Due to the strongly distorted dispersion near the gap, m c is suppressed by more than a factor of 3 near the upper gap edge, and enhanced by ∼50% near the lower gap edge, in excellent agreement with the theory of Lyo. We also observe the quantum Hall effect in a double QW at a high, constant B ⊥.