Coherent ultrafast spin-dynamics probed in three dimensional topological insulators.

Area of Science:

• Condensed matter physics
• Spintronics
• Materials science

Background:

• Topological insulators are promising for spintronics due to unique spin properties.
• Spin properties arise from spin-orbit interaction and momentum coupling, distinct from ferromagnetic exchange interactions.
• Light can control spin-polarization via the Dirac cone's energy-momentum landscape, enabling spin-momentum locking.

Purpose of the Study:

• Investigate light-induced spin signals in topological insulators.
• Disentangle spin and lattice contributions to optical signals.
• Demonstrate coherent femtosecond control of spin-polarization.

Main Methods:

• Studied the real and imaginary parts of the complex Kerr angle.
• Analyzed a spin-related signal present only during laser excitation.
• Characterized the signal using Raman coherence time, focusing on transitions at the conduction band edge.

Main Results:

• Identified a coherent, light-induced spin signal.
• The signal's behavior is linked to Raman coherence time.
• Demonstrated femtosecond control over spin-polarization of electronic states near the Dirac cone.

Conclusions:

• Coherent femtosecond control of spin-polarization is achievable in topological insulators.
• The observed phenomenon involves Raman coherence and light-matter interaction at the Dirac cone.
• This work opens avenues for novel optical control in spintronic devices.