Dipolar Order Induced Electron Spin Hyperpolarization.

Area of Science:

• Magnetic Resonance
• Quantum Information Science
• Chemical Physics

Background:

• Coupled electron spin systems are vital for dynamic nuclear polarization (DNP), enhanced nuclear magnetic resonance (NMR), and quantum information science (QIS).
• Characterizing electron spin coupling networks is challenging, particularly at high magnetic fields.
• Trityl radicals at high concentrations exhibit DNP enhancement profiles indicative of electron spin clusters.

Purpose of the Study:

• To investigate the mechanism of electron spin hyperpolarization in coupled electron spin systems using pump-probe ELectron DOuble Resonance (ELDOR).
• To demonstrate that selective microwave saturation can generate and characterize electron spin hyperpolarization.
• To explore the role of longitudinal dipolar order in transient electron spin hyperpolarization.

Main Methods:

• Utilizing pump-probe ELectron DOuble Resonance (ELDOR) experiments with selective microwave saturation.
• Analyzing ¹H NMR enhancement profiles to identify electron spin clusters.
• Investigating the influence of pulse lengths and interpulse delays on dipolar order generation and readout.

Main Results:

• Observed electron spin hyperpolarization upon selective microwave saturation in a trityl radical system.
• Demonstrated that the generation of out-of-equilibrium longitudinal dipolar order is responsible for electron spin hyperpolarization.
• Showed that coupled electron spins must form an AX-like system for selective microwave irradiation to induce hyperpolarization.
• Quantified the alteration of dipolar order by tuning ELDOR experimental parameters.

Conclusions:

• Pump-probe ELDOR with selective saturation is an effective method for characterizing coupled electron spins in AX-type spin systems.
• This technique is foundational for applications in DNP and quantum sensing.
• Understanding and controlling dipolar order is key to generating electron spin hyperpolarization.