9 May 2023 Tue 4 pm

Many recent experiments discovered chiral-induced spin selectivity (CISS): electrons scattered by helical organic molecules become spin-polarized. The theoretical explanation of this phenomenon is still under debate. Many theories start with spin-orbit interactions (SOIs) on the molecule, but the SOI preserves time-reversal symmetry, and therefore implies no spin selectivity in the linear conductance when the molecule connects two single channel terminals (Bardarson's theorem). Here we model the molecule by a tight-binding Hamiltonian, with a Rashba SOI along the helix and additional hopping in the direction of the helix axis, and present several ways to overcome the theorem and achieve CISS: allowing leakage from the molecular ions, adding a third terminal, adding magnetic fields, adding time-dependent potentials, adding more orbital states on the molecule, and various non-linear effects. All of these yield CISS, so we are still far from having a unique explanation. Recent alternative theories will be criticized.

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