Nonequilibrium Magneto-Conductance as a Manifestation of Spin Filtering in Chiral Nanojunctions

Abstract

It is generally accepted that spin-dependent electron transmission may appear in chiral systems, even without magnetic components, as long as significant spin–orbit coupling is present in some of its elements. However, how this chirality-induced spin selectivity (CISS) manifests in experiments, where the system is taken out of equilibrium, is still debated. Aided by group theoretical considerations and nonequilibrium DFT-based quantum transport calculations, here we show that when spatial symmetries that forbid a finite spin polarization in equilibrium are broken, a net spin accumulation appears at finite bias in an arbitrary two-terminal nanojunction. Furthermore, when a suitably magnetized detector is introduced into the system, the net spin accumulation, in turn, translates into a finite magneto-conductance. The symmetry prerequisites are mostly analogous to those for the spin polarization at any bias with the vectorial nature given by the direction of magnetization, hence establishing an interconnection between these quantities.

Magnetoconductance from spin-charge inter-conversion in two-terminal molecular nanojunctions with strong spin-orbit coupling electrodes.

“…where T (+M ) and T (−M ) are the transmission functions that have been obtained for the mutually reversed magnetizations of each system, calculated following the approach described in Ref. [10]. (The magnetization in the FM Ni layers point along the −z-axis in the reversed case.)…”

“…Instead, when finite, the multiplicative SOC factors are kept at values that give a good fit to the SOC bands of bulk FCC Ni. Those interested can find comprehensive information about our implementation of SOC in ANT.Gaussian in our previous publications [9,10,35,37]. as insets here).…”

“…In the realm of the chirality-induced spin selectivity (CISS) phenomenon, these measurements offer valuable perspectives on the spin-specific transport characteristics of chiral systems [1][2][3][4][5][6][7][8]. By examining the variation in conductance with changes in the magnetic field in suitably designed experiments [6,8], information can be gathered about the spin selectivity in chiral systems that are ultimately induced by spatial symmetry-breaking [9,10].…”

Role of Electrode Polarization in the Electron Transport Chirality-Induced Spin-Selectivity Effect

“…To date, elucidating the origin of the CISS effect is considered to be an outstanding open problem. , While many different theoretical proposals for the origin of CISS were put forward, there is an active ongoing debate, and a clear picture is yet to emerge. One can divide the suggested mechanisms pertaining to the transport-manifestation of the CISS effect into two main groups, namely theories based on spin–orbit coupling (SOC) in noninteracting electrons (e.g. − ), and theories based on some form of interaction; magnetic, , electron–phonon, − Coulomb interactions, , and more. − …”

Spin–Orbit Torque in Single-Molecule Junctions from ab Initio

“…We display in Figure the nonequilibrium self-consistency cycle; the technical details have been relegated to the Supporting Information (SI). In short, starting from an optimized geometry of the molecular junction obtained with the FHI-aims package, we perform a self-consistent DFT , -NEGF , cycle that accounts for the charge redistribution in the junction due to the macroscopic nature of the contacts. ,− We ensure the charge neutrality and screening the excess charge accumulated at the boundaries of the finite cluster by a self-energy model implemented in the module AITRANSS. ,, This module was recently extended to include SO coupling . Our self-consistent scheme thus expands available DFT-NEGF self-consistent cycles. ,,,− …”