Dynamic nuclear polarization (DNP) refers to the transfer of high electron polarization (due to the robust electron gyromagnetic ratio gamma=28,000 MHz/T) to the nuclear spins at low temperature (close to 1 K) and high magnetic field (> 1 T) via microwave irradiation close to the ESR frequency of the free radical. By employing a fast dissolution method, the solid state sample containing the hyperpolarized target nuclei (e.g. biologically-important 13C and 15N molecules) is rapidly converted into a solution at physiological temperature. Due to the long spin-lattice relaxation time T1 of the nuclei of interest, the nuclear polarization is preserved which allows, for the first time, magnetic resonance imaging (MRI) of low-gamma nuclei such as 13C, 15N, 6Li, 89Y, among others.
Condensed Matter Physics
NMR is an excellent microscopic probe of magnetism and electronic properties of materials because the nuclear spins act as “spies” to the workings of the surrounding electrons which are responsible for most of the properties of condensed matter systems. One class of materials that is rich in electron physics is the quasi-one-dimensional (Q1D) system—materials that exhibit electronic instabilities such as spin density waves (SDW) and charge density waves (CDW). Q1D materials make a phase transition from metallic state to SDW/CDW insulating states below a certain critical temperature Tc. Below Tc, these materials lose their Fermi surfaces because of the appearance of an energy gap. The bulk of my graduate work was devoted to the investigation of such materials using NMR and electrical transport techniques as the main probes (picture: submillimeter NMR coil and four-contact gold wire transports leads in the organic superconductor (TMTSF)2ClO4).