Electrical and thermal transport through $α-T_3$ NIS junction

We investigate the electrical and thermal transport properties of the $α-T_3$ based normal metal-insulator-superconductor (NIS) junction using Blonder-Tinkham-Klapwijk (BTK) theory. We show that the tunneling conductance of the NIS junction is an oscillatory function of the effective barrier potential ($χ$) of the insulating region upto a thin barrier limit. The periodicity and the amplitudes of the oscillations largely depend on the values of $α$ and the gate voltage of the superconducting region, namely, $U_0$. Further, the periodicity of the oscillation changes from $π$ to $π/2$ as we increase $U_0$. To assess the thermoelectric performance of such a junction, we have computed the Seebeck coefficient, the thermoelectric figure of merit, maximum power output, efficiency at the maximum output power of the system, and the thermoelectric cooling of the NIS junction as a self-cooling device. Our results on the thermoelectric cooling indicate practical realizability and usefulness for using our system as efficient cooling detectors, sensors, etc., and hence could be crucial to the experimental success of the thermoelectric applications of such junction devices. Furthermore, for an $α-T_3$ lattice, whose limiting cases denote a graphene or a dice lattice, it is interesting to ascertain which one is more suitable as a thermoelectric device and the answer seems to depend on the $U_0$. We observe that for an $α-T_3$ lattice corresponding to $U_0=0$, graphene ($α=0$) is more feasible for constructing a thermoelectric device, whereas for $U_0 \gg E_F$, the dice lattice ($α=1$) has a larger utility.

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