Spin-dependent transport properties and Seebeck effects for a crossed graphene superlattice p-n junction with armchair edge
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Using the nonequilibrium Green’s function method combined with the tight-binding Hamiltonian, we theoretically investigate the spin-dependent transmission probability and spin Seebeck coefficient of a crossed armchair-edge graphene nanoribbon (AGNR) superlattice p-n junction under a perpendicular magnetic field with a ferromagnetic insulator, where junction widths W1 of 40 and 41 are considered to exemplify the effect of semiconducting and metallic AGNRs, respectively. A pristine AGNR system is metallic when the transverse layer m = 3j + 2 with a positive integer j and an insulator otherwise. When stubs are present, a semiconducting AGNR junction with width W1 = 40 always shows metallic behavior regardless of the potential drop magnitude, magnetization strength, stub length, and perpendicular magnetic field strength. However, metallic or semiconducting behavior can be obtained from a metallic AGNR junction with W1 = 41 by adjusting these physical parameters. Furthermore, a metal-to-semiconductor transition can be obtained for both superlattice p-n junctions by adjusting the number of periods of the superlattice. In addition, the spin-dependent Seebeck coefficient and spin Seebeck coefficient of the two systems are of the same order of magnitude owing to the appearance of a transmission gap, and the maximum absolute value of the spin Seebeck coefficient reaches 370 µV/K when the optimized parameters are used. The calculated results offer new possibilities for designing electronic or heat-spintronic nanodevices based on the graphene superlattice p-n junction.
Keywordscrossed graphene superlattice p-n junction spin-dependent transport properties Seebeck coefficient nonequilibrium Green’s function
PACS numbers73.22.-f 73.63.-b 72.25.Dc 79.10.-n
This work was supported by the National Natural Science Foundation of China (Grant Nos. 11704118, 11774085, and 11404230), the Scientific Research Fund of Hunan Provincial Education Department (Grant Nos. 17A193 and 17C0946), the Hunan Provincial Natural Science Foundation of China (Grant No. 2017JJ3210), and the Foundation of Science and Technology Bureau of Sichuan Province (No. 2013JY0085).
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