Exploring large coherent spin systems with solid state NMR

Abstract

Solid state Nuclear Magnetic Resonance (NMR) allows us to explore a large coherent spin system and provides an ideal test-bed for studying strongly interacting multiple-spin system in a large Hilbert space. In this thesis, we experimentally investigate the spin dynamics in a rigid lattice of dipolarly coupled nuclear spins using multiple quantum NMR spectroscopy. Encoding multiple quantum coherences (MQC) in an arbitrary quantizing axis is developed. We utilized this method to encode coherence numbers in an orthogonal basis to Zeeman basis and showed that the dipolar-ordered state is a two spin correlated state, and confirmed the presence of the ... (flip-flop) terms in the experimentally prepared dipolar-ordered state. A new experimental investigation of the problem of the NM:R free induction decay (FID) in a lattice of spin 1/2 nuclei is presented to verify the multi-spin nature of the FID and the dominant role of the geometrical arrangement of the spins in the development of higher order correlations under the dipolar evolution. To study the dynamics and the controllability of these multiple spin correlations, effective decay times of individual coherence orders are measured under the dipolar interaction and under the control sequence that suppresses the dipolar evolution.

(cont.) It is seen that the decay time of each coherence order becomes shorter and more uniform among different coherence orders as the spin correlation size grows larger in both cases. Additional work has been done in this thesis, toward creating a pure state in solid state nuclear spins by transferring polarization from electron spins, i.e Dynamic Nuclear Polarization (DNP). A new cryogenic DNP probe was developed enabling multiple pulse irradiations at low temperature with enhanced polarization.