Tunable many-body effects in triple quantum dots

Abstract

Exchange energies and charge densities for a few electrons in electrically tunable triangular and collinear triple quantum dot (TQD) systems are investigated by using the variational Monte Carlo method in the presence of magnetic fields. For N = 2 electrons we observe a discontinuity in the J derivative with detuning voltage (dJ/dV(T)) in triangular triple QDs at B= 0 T as crossing of the eigenenergy levels leads to abrupt spatial symmetry change in the singlet and the triplet densities (density rotation) and relocalization. For B not equal 0 T, the angular momentum provided to the electrons quenches this effect. The density rotation is absent in the collinear TQD for all magnetic fields as the lowest excited state remains the p(x) state and as such, no change in symmetry is possible. By varying the triangular TQD configuration, we show the discontinuity in dJ/dV(T) persists for the top angle comprised between similar to 20 degrees and similar to 70 degrees. For three electrons in the symmetric triangular TQD, the monotonicity of the quadruplet-doublet energy difference from B = 0 to 4 T remains intact for decoupled QDs but not for coupled QDs. Finally, addition energy for the triangular TQD system is computed for up to N = 3 electrons.