Strong nonlinear thermoelectricity generation and close-to-Carnot efficient heat engines in Superconductor-Insulator-2D electron gas junctions

We propose and theoretically analyse a novel Superconductor-Insulator-2D electron gas tunnel junction (SI2DEG) that strongly and efficiently generates thermoelectricity via a nonlinear mechanism. By varying the position of the electrochemical potential of the 2DEG, the SI2DEG junction shows different thermoelectric generation regimes with performance exceeding state-of-the-art tunnel systems. Indeed, the generated Seebeck potential can reach $6.75\Delta_0/e$ with a nonlinear Seebeck coefficient as high as $\mathcal{S}=5\,\Delta_0/e{\rm K}$. When operated as a quantum heat engine, the system efficiency gets very close to the Carnot limit with a maximum value $\eta=0.92\eta_C$ with a non-negligible power output. The SI2DEG junction also shows peculiar features such as bidirectional cooling controlled by the potential bias and bistability of the thermoelectric generation. These features, together with its strong temperature response, make the SI2DEG system an interesting general platform for quantum science and technology applications, such as quantum thermodynamics, ultrasensitive cosmology and dark-matter detection, and qubit refrigeration.