Signatures of d-Wave Symmetry on Thermal Dirac Fermions in Graphene-Based F/I/d Junctions

Abstract

We study theoretically the behavior of thermal massless Dirac fermions inside graphene-based Ferromagnetic/Insulator/d-wave (s-wave) superconductor (F/I/d and F/I/S) junctions in the ballistic regime. Using the Dirac-BdG wave functions within the three regions and appropriate boundary conditions, the Andreev and Normal reflection coefficients are derived. By employing the obtained Andreev and Normal reflection coefficients the characteristics of heat current through the F/I/d and F/I/S junctions are investigated within the thin barrier approximation. We find that for s-wave superconductors, thermal conductance oscillates sinusoidally vs barrier strength. The finding persist for the values of $\alpha$, the orientation of d-wave superconductor crystal in the $k$-space, below $\pi /4$. By increasing temperature, the thermal conductance is increased exponentially for small values of $\alpha$ and for larger values the quantity is modified to exhibit a linear behavior at $\alpha =\pi /4$ which is similar to Wiedemann-Franz law for metals in low temperatures.

6 pages, 6 figures

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