2009/12/23 by Ya-Fen Hsu, Guang-Yu Guo, Guang‐Yu Guo
Materials Science · Physics and Astronomy · #Amplitude #Condensed matter physics #Conductance #Dirac fermion #Electron #Fermi energy #Graphene #Graphene research and applications #Physics #Quantum and electron transport phenomena #Quantum mechanics #Quantum tunnelling #Superconductivity #Topological Materials and Phenomena #cond-mat.mes-hall
paper · pdf · doi:10.1103/physrevb.81.045412
published as Physical Review B 81, 045412 (2010) · Accepted for publication in Physical Review B
arxiv created 2009/12/23 · openalex publication_date 2010/01/13 · arxiv updated 2015/05/14 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We study the transport properties of a graphene ferromagnet-insulator-superconductor (FIS) junction within the Blonder-Tinkham-Klapwijk formalism by solving spin-polarized Dirac-Bogoliubov-de-Gennes equation. In particular, we calculate the spin polarization of tunneling current at the I-S interface and investigate how the exchange splitting of the Dirac fermion bands influences the characteristic conductance oscillation of the graphene junctions. We find that the retro- and specular Andreev reflections in the graphene FIS junction are drastically modified in the presence of exchange interaction and that the spin polarization (PT) of tunneling current can be tuned from the positive to negative value by bias voltage (V). In the thin-barrier limit, the conductance G of a graphene FIS junction oscillates as a function of barrier strength \ensuremathχ. Both the amplitude and phase of the conductance oscillation varies with the exchange energy Eex. For Eex<EF (Fermi energy), the amplitude of oscillation decreases with Eex. For Eexc>Eex>EF, the amplitude of oscillation increases with Eex, where Eexc=2EF+U0 (U0 is the applied electrostatic potential on the superconducting segment of the junction). For Eex>Eexc, the amplitude of oscillation decreases with Eex again. Interestingly, a universal phase difference of \ensuremathπ/2 in \ensuremathχ exists between the G\text\ensuremath-\ensuremathχ curves for Eex>EF and Eex<EF. Finally, we find that the transitions between retro- and specular Andreev reflections occur at eV=|EF\ensuremath-Eex| and eV=Eex+EF, and hence the singular behavior of the conductance near these bias voltages results from the difference in transport properties between specular and retro-Andreev reflections.