Assessment of heteronuclear long-lived states at ultralow magnetic fields.

A study of long-lived spin states in hetero-nuclear spin systems is presented. Since long-lived states are efficiently sustained only when the spins are "strongly coupled", this study necessitates going to "ultralow" magnetic fields, which are much lower than the Earth's field. To do so, we utilize a fast field-cycling device, which rapidly shuttles the sample between an NMR (Nuclear Magnetic Resonance) magnet and a magnetic shield with a very low field inside. While the spin evolution is taking place at an ultralow field, detection is performed at the high field of an NMR spectrometer. We report hetero-nuclear long-lived order in two spin and four-spin systems, given by the CH and CH3 groups of methyl propiolate, and present a detailed analysis of the spectral manifestation of such long-lived states.