Efficiency of three-terminal thermoelectric transport under broken time-reversal symmetry

We investigate thermoelectric efficiency of systems with broken time-reversal symmetry under a three-terminal transport. Using a model of Aharonov-Bohm interferometer formed with three noninteracting quantum dots, we show that Carnot efficiency η_C can be achieved when the thermopower is a symmetric function of the applied magnetic field. On the other hand, the maximal value of the efficiency at maximum power is obtained for asymmetric thermopower. Indeed, we show that the Curzon-Ahlborn limit is exceeded within the linear response regime in our model. Moreover, we investigate thermoelectric efficiency for random Hamiltonians drawn from the Gaussian unitary ensemble and for a more abstract transmission model. In this latter model, we find that the efficiency is improved using sharp energy-dependent transmission functions.