Generating Spin Echoes with Pi-Pulses: More is Different
ORAL
Abstract
NMR spin echo measurements in several solids linked through the form of the homonuclear dipolar coupling are shown to defy conventional expectations of the delta-function pulse approximation. Multiple pi-pulse echo trains may either freeze-out or accelerate the decay of the signal, depending upon pi-pulse phase. Average Hamiltonian theory, combined with exact quantum calculations, reveal an intrinsic cause for these coherent phenomena: the dipolar coupling has a many-body effect during any real, finite pulse.
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