Exchange energy in vertically coupled double quantum dots

The exchange separation between spin singlet and triplet states was studied for vertically coupled double quantum dots in the Pauli spin blockade regime with the inter-dot level detuning as a parameter. Pauli blockade is established by the formation of an excited but long-lived triplet state in the double dot, and is lifted by a spin flip transition to the singlet state, generating a leakage current. The leakage current shows a step when the Zeeman energy equals the exchange energy thus turning on the flip-flop interaction with the nuclei. The threshold magnetic field increases on approaching the anti-crossing of the two triplets reflecting the increased exchange energy. We present a quantitative comparison of the exchange energy derived experimentally with exact theory.