Orbitronics: light-induced orbital currents in Ni studied by terahertz emission experiments

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics and Orbitronics

Background:

• Orbitronics utilizes orbital currents as information carriers, with established methods for generating them from charge or spin currents.
• The inverse conversion of orbital currents back to charge or spin currents is also a known phenomenon.

Purpose of the Study:

• To demonstrate the generation of orbital currents using femtosecond light pulses on nickel.
• To investigate the detection and characteristics of these light-induced orbital currents and their conversion into charge currents.
• To explore the potential of these findings for developing new orbitronic devices, particularly in the terahertz regime.

Main Methods:

• Fabrication of multilayer structures combining nickel with oxides and nonmagnetic metals like copper.
• Utilizing femtosecond laser pulses to induce orbital currents in the nickel layers.
• Detecting orbital currents through their conversion into charge currents, evidenced by terahertz emission.
• Analyzing the time delays of terahertz pulses to determine orbital carrier velocity and propagation length.

Main Results:

• Successfully generated and detected light-induced orbital currents in nickel-based systems.
• Observed that orbital currents significantly predominate over light-induced spin currents in Ni-based materials.
• Demonstrated the conversion of orbital currents into charge currents, leading to terahertz emission.
• Obtained insights into the velocity and propagation length of orbital carriers through time-resolved terahertz emission analysis.
• Contrasted findings with CoFeB-based systems, where only spin currents were detected.

Conclusions:

• The study establishes a novel method for generating orbital currents using light pulses, expanding the toolkit for orbitronics.
• The predominant nature of orbital currents over spin currents in Ni-based systems offers unique advantages for device applications.
• The observed light-induced orbital currents and their conversion to charge currents open new pathways for developing advanced orbitronic terahertz devices.