Fig. 2. Early onset of ν = −1 QH plateau in a (Hg,Mn)Te QW.

(A) The longitudinal (R_xx) and transverse resistance (R_xy) of Dev 1 are depicted as a function of perpendicular magnetic field B_⊥ at 20 mK for normalized gate voltage $V_g^{*}=V_g-V_d=0$ V. The inset shows the resistance R_xx as a function of $V_g^{*}$ at 20 mK and B_⊥ = 0 mT. The shaded region corresponds to the bulk p-regime. (B) R_xy as a function of B_⊥ for $V_g^{*}$ ranging from −0.4 to 0.28 V (near the QSH regime) at 20 mK for Dev 1. The dotted line shows the ν = −1 QH plateau. The inset schematically shows the chemical potential μ in the bulk gap. (C) Band structure computed using k · p theory on a strip of width 500 nm (confinement in the z and y directions) at B_⊥ = 0 mT. (D) Band structure for B_⊥ = 100 mT. The expectation values 〈y〉 (extracted from eigenstates) represent the in-plane “location” of the state. Edge states are shown in red and blue, while bulk states are shown in gray. The topological gap (filling factor ν = 0 regime) and the magnetic gap with ν = −1 are shaded in green and yellow, respectively.