Evidence of spin-temperature in dynamic nuclear polarization: an exact computation of the EPR spectrum

Filippo Caracciolo 1 Marta Filibian 1 Pietro Carretta 1 Alberto Rosso 2 Andrea De Luca 2

PCCP : Physical chemistry chemical physics, Royal Society of Chemistry, 2016, 18, pp.25655

In a dynamic nuclear polarization (DNP) procedure, the compound is driven out-of-equilibrium by microwave irradiation of the dipolar electron spins of the radical. The main outcome of this protocol is the huge polarization enhancement for nuclear spins. In this paper, we focus on the steady-state polarization of the electron spins, which is experimentally accessible via ELDOR techniques. By varying the radical concentration, two scenarios emerge: for dilute samples, the irradiated ELDOR spectrum displays the narrow hole-burning profile predicted by Bloch equations; for higher concentrations, the ELDOR spectrum is completely reorganized according to the spin-temperature description. We discuss our results in relation with recent EPR experiments and, in particular, we analyze the dependence on the microwave intensity.

  • 1. CNISM - Dipartimento di Fisica and Unità
  • 2. LPTMS - Laboratoire de Physique Théorique et Modèles Statistiques