Figure 4: Spin blockade and exchange energy at the (1, 3)–(0, 4) charge transition.
(a) Stability diagram with B=0 T, with interdot tunnelling between the (1, 3) and (0, 4) charge configurations. The arrow indicates the direction of increasing detuning energy ɛ. (b) Same diagram taken with B=2 T. The interdot phase response disappears as the ground state of the system is now a triplet. (c) Energy level diagram for the system, including three spin triplet states with (1, 3) charge configuration (blue) and two singlet states (red). With applied magnetic field the ground-state transitions from singlet to triplet at detuning energy ɛD. (d) Phase response at the interdot transition as a function of detuning, a cut through the data of a along the detuning line. The red curve indicates a fit to equation (4) from which we extract the tunnel coupling tc=47 μeV. (e) Interdot phase measurement as a function of detuning ɛ and magnetic field B. The phase response disappears asymmetrically as the exchange energy increases for increasing ɛ. The dashed line indicates the degeneracy of the lowest energy singlet and triplet states.
