Surface-State-Dominated Spin-Charge Current Conversion in Topological-Insulator-Ferromagnetic-Insulator...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Topological insulators (TIs) possess unique spin-momentum locked surface states.
• Spin-charge conversion is a key phenomenon in spintronics for developing novel devices.
• Heterostructures of TIs and ferromagnets are promising for exploring spin-charge interconversion.

Purpose of the Study:

• To investigate ferromagnetic resonance (FMR)-driven spin pumping in TI/ferromagnet heterostructures at room temperature.
• To determine the influence of TI film thickness on spin-charge conversion efficiency.
• To elucidate the role of surface states in the spin-charge interconversion process.

Main Methods:

• Fabrication of Bi_{2}Se_{3} and (Bi,Sb)_{2}Te_{3} thin films on Y_{3}Fe_{5}O_{12} using molecular beam epitaxy.
• Ferromagnetic resonance (FMR) measurements to detect spin pumping signals.
• Systematic variation of TI film thickness to study its effect on spin-charge conversion.

Main Results:

• Observation of FMR-driven spin pumping signals at room temperature.
• Significant increase in inverse Rashba-Edelstein effect length (λ_{IREE}) with increasing Bi_{2}Se_{3} thickness up to six quintuple layers.
• Saturation of λ_{IREE} for thicknesses above six quintuple layers, indicating dominant surface state contribution.

Conclusions:

• Surface states of topological insulators play a crucial role in spin-charge interconversion in TI/ferromagnet heterostructures.
• The observed phenomena are consistent across different TI materials like Bi_{2}Se_{3} and (Bi,Sb)_{2}Te_{3}.
• Effective interfacial spin mixing conductance and λ_{IREE} can be determined from FMR linewidth broadening and spin pumping signals.