Unusual Spin Polarization in the Chirality-Induced Spin Selectivity

Area of Science:

• Condensed matter physics
• Molecular electronics
• Spintronics

Background:

• Chirality-induced spin selectivity (CISS) is a phenomenon where electrons become spin-polarized after interacting with chiral molecules.
• Existing models often describe chiral molecules as spin filters, allowing one spin to pass while reflecting the other.

Purpose of the Study:

• To re-evaluate the established understanding of CISS.
• To clarify the role of chiral molecules in spin polarization phenomena.
• To reconcile CISS with fundamental principles of equilibrium spin currents.

Main Methods:

• Theoretical analysis of electron transport through chiral molecules in nanoscale devices.
• Examination of spin polarization in both transmitted and reflected electron currents.
• Consideration of equilibrium conditions and spin-orbit coupling effects.

Main Results:

• Chiral molecules act as spin polarizers, not spin filters, meaning transmitted and reflected electrons exhibit the same spin polarization.
• The spin polarization direction depends on molecular chirality and electron incidence.
• The magnitude of spin polarization is influenced by local spin-orbit coupling.

Conclusions:

• The study provides a revised understanding of CISS, aligning it with the principle that equilibrium spin currents must be zero.
• This work offers a new perspective for interpreting experimental observations, including the CISS-driven anomalous Hall effect.