Controlling Magnetism with Light in a Zero Orbital Angular Momentum Antiferromagnet

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Antiferromagnetic materials exhibit ultrafast spin dynamics, crucial for THz frequency magnonic devices.
• Optical generation of coherent magnons in antiferromagnetic insulators is a key research area.
• Spin-orbit coupling facilitates spin dynamics via resonant excitation of electric dipoles in systems with orbital angular momentum.

Purpose of the Study:

• To investigate optical methods for controlling spin dynamics in antiferromagnetic insulators lacking orbital angular momentum.
• To compare the efficacy of electronic versus vibrational excitations for optical spin control in these materials.
• To identify microscopic pathways for low-energy optical excitation of coherent spin dynamics in zero orbital angular momentum magnets.

Main Methods:

• Experimental investigation of manganese phosphorous trisulfide (MnPS_{3}), an antiferromagnet with orbital singlet Mn^{2+} ions.
• Studying the correlation between spin dynamics and two types of intra-band-gap excitations: bound electron orbital transitions and vibrational excitations.
• Analyzing the effect of exciting Mn^{2+} from its singlet orbital ground state to an orbital triplet state.

Main Results:

• A bound electron orbital excitation induces coherent spin precession in MnPS_{3}.
• Vibrational excitation of the crystal field leads to thermal spin disorder, not coherent dynamics.
• Orbital transitions are identified as the primary mechanism for optical control of spin dynamics in this material class.

Conclusions:

• Orbital transitions are critical for achieving optical control of spin dynamics in antiferromagnetic insulators with magnetic centers of zero orbital angular momentum.
• This finding offers a new pathway for designing and manipulating ultrafast spin dynamics in novel magnetic materials.
• The results highlight the potential of exploiting electronic orbital excitations for future THz magnonic devices.