arXiv subjects

Takemitsu Kato

Publications and source records attributed to Takemitsu Kato.

3 recordsLinked to original sources

arXiv2025

Interatomic spin-orbit interaction in a $p$-orbital helical atomic chain

We derive the interatomic spin-orbit interaction (SOI) from a helical atomic chain composed of $p$-orbitals with intra-atomic SOI, which exhibits a helical state--a potential origin of the chiral-induced spin selectivity (CISS) effect. In this model, a strong crystal field in the tangential direction of the helix leads to the formation of energetically separated $\sigma$- and $\pi$-bands. In the second-order process, a spin in the $\sigma$-orbital virtually hops to the $\pi$-orbital, flips its direction due to intra-atomic SOI, and then hops back to the $\sigma$-orbital in the neighboring atom due to the misalignment of $p$-orbitals along the helix. This process induces an interatomic SOI in the $\sigma$-band, which takes the form of a Rashba-type SOI generated by an electric field normal to the helical axis. The magnitude of the SOI is proportional to the curvature, the hopping energy, the intra-atomic SOI energy, and inversely proportional to the crystal field strength. The second-order process also induces long-range second-nearest-neighbor hoppings. We analytically derive the spin-split band structure in the zero-torsion limit.

cond-mat.mes-hall↗

arXiv2023

Electronic and Spin States at Edges of Finite $p$-orbital Helical Atomic Chain

In connection to the chiral-induced spin-selectivity (CISS) effect, we theoretically analyze the electronic and spin states of edges of a finite $p$-orbital helical atomic chain with the intra-atomic spin-orbit interaction (SOI). This model can host the spin-filtering state in which two up spins propagate in one direction and two down spins propagate in the opposite direction without breaking the time-reversal symmetry. The enhancement of charge modulations concentrated at the edges due to the evanescent states is induced, although the spin density is absent because of the time-reversal symmetry (TRS). A Zeeman field at an edge of the atomic chain, which breaks the TRS, yields a finite spin polarization, whose direction depends on the chirality of the molecule. The chirality change induces a reasonable amount of the energy difference, which may provide an insight into the enantioselective adsorption of chiral molecules on the ferromagnetic surface.

cond-mat.mes-hall↗

arXiv2022

Spin-filtering in a $p$-orbital helical atomic chain

We theoretically analyze spin filtering in two-terminal systems, induced by the spin-orbit interaction (SOI), as a possible origin of the ``chirality-induced spin selectivity'' (CISS) effect observed experimentally in chiral molecules, such as DNA. Due to Bardarson's theorem, spin filtering cannot be realized in a molecule containing one orbital-channel. However, when two orbitals are involved, SOI can induce spin filtering in a molecule coupled to two terminals without braking time-reversal symmetry. In particular, we provide an example of a $4 \times 4$ reflection matrix for a spinful electron passing through a molecule containing two orbital-channels, which complies with Bardarson's theorem and produces a finite spin conductance. As a microscopic toy model realizing a single strand of DNA, we consider a $p$-orbital helical atomic chain with intra-atomic SOI's and a strong crystalline field along the helix. This model exhibits two-orbital spin filtering: For various parameters preserving the helical symmetry, the model hosts spin asymmetric states carrying pairs of up and down spins propagating in opposite directions. The typical energy scale of the helical states is the product of the intra-atomic SOI and the curvature. The large value of this energy identifies our model as a likely candidate to explain the CISS in organic molecules.

cond-mat.mes-hall↗