Andreev reflection and Josephson effect in the $α$-T3 lattice

Abstract: We investigate the Andreev reflection and Josephson effect in the $\alpha$-T3 lattice which falls between graphene ($\alpha = 0$) and the dice lattice ($\alpha = 1$) by adjusting the parameter $\alpha$. In the regime of specular Andreev reflection, when the incident energy of electron is small, the probability of Andreev reflection decreases as the parameter $\alpha$ increases. On the contrary, when the incident energy is large, the probability of Andreev reflection increases as the parameter $\alpha$ increases. Interestingly, when the incident energy approaches the superconducting energy-gap function, the Andreev reflection with approximate all-angle perfect transmission happens in the case of $\alpha = 1$. In the regime of Andreev retro-reflection, when the parameter $\alpha$ increases, the probability of Andreev reflection increases regardless of the value of incident energy. When the incident energy approaches the superconducting energy-gap function, the Andreev reflection with approximate all-angle perfect transmission happens regardless of the value of $\alpha$. We also give the differential conductance in these two regimes and find that the differential conductance increases as the parameter $\alpha$ increases generally. In addition, the $\alpha$-T3 lattice-based Josephson current increases as $\alpha$ increases. When the length of junction approaches zero, the critical Josephson currents in the different values of $\alpha$ approach the same value.