Analytical model for spin dynamics in radical pairs under the spin-locking condition

Area of Science:

• Chemical Physics
• Quantum Mechanics

Background:

• Triplet radical pairs exhibit complex spin dynamics.
• Spin-locking conditions are used to control these dynamics by blocking singlet-triplet mixing with resonant microwave fields.

Purpose of the Study:

• To theoretically investigate spin dynamics in triplet radical pairs under spin-locking conditions.
• To explore the implications of simultaneous T+-T0 and T--T0 transition excitations.

Main Methods:

• Theoretical analysis using a three-state model.
• Application of spin dynamics theory under resonant microwave fields.

Main Results:

• Triplet states are shown to be quantized along the microwave-induced magnetic field (B1) in the rotating frame.
• A novel spin-locking phenomenon is identified, with enhanced T+-T0 and T--T0 mixing occurring at magnetic fields deviating from resonance by ±B1.
• Quantum beats observed under spin-locking are attributed to the spin dynamics within triplet radical pairs.

Conclusions:

• The three-state model effectively describes spin dynamics in triplet radical pairs under spin-locking.
• The newly identified spin-locking phenomenon provides a deeper understanding of spin control in radical pairs.
• This work elucidates the origin of quantum beats in such systems.