Bulk Rashba-Type Spin Splitting in Non-Centrosymmetric Artificial Superlattices

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Efficient charge-to-spin conversion is vital for spintronic devices like magnetic random-access memory.
• Current methods often rely on spin Hall or Rashba effects, with high conversion efficiency being a key requirement.
• Artificial superlattices offer tunable properties for novel spintronic functionalities.

Purpose of the Study:

• To demonstrate and investigate bulk Rashba-type charge-to-spin conversion in centrosymmetric artificial superlattices.
• To explore the dependence of charge-to-spin conversion on layer thickness, specifically in [Pt/Co/W] superlattices.
• To understand the origin of enhanced spin-transfer torque through first-principles calculations.

Main Methods:

• Fabrication of [Pt/Co/W] artificial superlattices with sub-nanometer layer thicknesses.
• Experimental measurement of charge-to-spin conversion efficiency and field-like torque.
• First-principles calculations to elucidate the underlying physical mechanisms.

Main Results:

• Demonstration of bulk Rashba-type charge-to-spin conversion in a non-centrosymmetric superlattice.
• Significant W thickness dependence observed, with optimal performance at 0.6 nm.
• Field-like torque efficiency of approximately 0.6 achieved, an order of magnitude higher than in other metallic heterostructures.
• First-principles calculations confirm bulk Rashba effect due to broken inversion symmetry from W layers as the source of high torque.

Conclusions:

• The [Pt/Co/W] superlattice exhibits a highly efficient bulk Rashba-type charge-to-spin conversion mechanism.
• Vertically broken inversion symmetry in W layers is identified as the key factor for enhanced spin-transfer torque.
• Artificial superlattices provide a promising platform for engineering spin-splitting bands to achieve superior charge-to-spin conversion for future spintronic applications.