Resonant Mixing Dynamic Nuclear Polarization

We propose a new mechanism for dynamic nuclear polarization that is different from the well-known Overhauser effect, solid effect, cross effect and thermal mixing processes. In particular, we discovered that the evolution of the density matrix with the simple Hamiltonian of a coupled electron-nuclear spin pair with weak microwave irradiation yields a nuclear polarization enhancement when irradiating near the electron Larmor frequency. We denote the mechanism as Resonant Mixing (RM). We believe that this mechanism is responsible for the observed dispersive shaped DNP field profile for trityl samples near the electron paramagnetic resonance center. This new effect is due to mixing of states by the microwave field together with the electron-nuclear coupling, and involves the same interactions as the SE. However, the SE is optimal when the microwave field is off-resonance, whereas RM is optimal when the microwave field is on-resonance.