Spin dynamics in helical molecules with nonlinear interactions

Abstract

It is widely admitted that the helical conformation of certain chiral molecules may induce a sizable spin selectivity observed in experiments. Spin selectivity arises as a result of the interplay between a helicity-induced spin-orbit coupling (SOC) and electric dipole fields in the molecule. From the theoretical point of view, different phenomena might affect the spin dynamics in helical molecules, such as quantum dephasing, dissipation and the role of metallic contacts. With a few exceptions, previous studies usually neglect the local deformation of the molecule about the carrier, but this assumption seems unrealistic to describe charge transport in molecular systems. We introduce an effective model describing the electron spin dynamics in a deformable helical molecule with weak SOC. We find that the electron-lattice interaction allows the formation of stable solitons such as bright solitons with well defined spin projection onto the molecule axis. We present a thorough study of these bright solitons and analyze their possible impact on the spin dynamics in deformable helical molecules.

Effective nonlinear model for electron transport in deformable helical molecules

“…Indeed, by increasing the number of dipoles per turn, we recover the solution of the continuum approximation. Our results provide further support to previous studies devoted to spin-transport in organic molecules such as DNA or α helices, where the continuum approximation was considered [6,12,22].…”

“…Since the number of dipoles per turn is usually much larger than unity in most cases of interest (N d 1), the continuum limit of the generalized Kronig-Penney model is a reasonable approximation and we are then led to an extended Davydov model, as discussed in Ref. [22].…”

“…A thorough study of the soliton solutions have been presented and discussed in Refs. [21,22]. In the following section we discuss how bright solitons, similarly to the wellknown Davydov's soliton [29], are affected when Eq.…”

“…In addition, the local deformation of the molecule about the carrier gives rise to nonlinear effects that ultimately can lead to self-trapping [20]. Nevertheless, theoretical models have taken into account the effects of molecular deformation and nonlinear interactions only very recently [21][22][23][24].…”

Thermal Decoherence and Disorder Effects on Chiral-Induced Spin Selectivity

“…Chiral-induced spin selectivity (CISS) is an intriguing physical effect, first experimentally demonstrated in 1999, that manifests itself as spin-dependent transport in helical albeit nonmagnetic molecules. [1][2][3] Despite the large amount of experimental [4][5][6][7][8][9][10][11][12][13][14][15][16] and theoretical [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] work published so far, the ultimate origin of the CISS effect is still subject to debate. There seems to be, however, agreement that a combination of the helical conformation of the molecule, together with field and exchange effects, leads to an enhanced spin-orbit interaction that ultimately is responsible for the spin-dependent transmission of electrons in media without time reversal symmetry.…”