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[PAST EVENT] Physics & Applied Science Colloquium
November 9, 2012
4pm - 5pm
Abstract:
An important question for many-body systems is how microscopic quantum mechanical parameters influence a corresponding dynamic at the macroscopic scale. Single crystal of calcium fluoride is an ideal test system for experimental investigation of such phenomenon-the spin degrees of freedom are well defined, relaxation times can be very long, and internal dynamics such as spin diffusion are kinematically simple. Experimentally, one can control the nuclear spin system by average Hamiltonian theory, developed by J. S. Waugh and coworkers, to study how a microscopic quantum property such as a spin state affects a macroscopic observable, such as a spin diffusion rate. A method of measuring diffusion in magnetic resonance is to encode a spatial modulation of magnetization in a sample and then measure it's attenuation over time. The difficulty in measuring spin diffusion in solid crystals by these scattering methods is that the spin diffusion rate is very slow (of an order 1 x 10^-12 cm^2/s) and hence the displacement of spin coherence is very small (approximately 1 micron per hour). The experimental challenge for probing these dynamics is that a spatial modulation of the nuclear spin magnetization must be created with a wavelength on these length scales. In this talk I will describe the method by which spin diffusion can be measured, in addition to a scheme by which the homonuclear dipolar Hamiltonian can be effectively turned-off in NMR using average Hamiltonian methods. The talk will include a discussion of the measurement of the spin diffusion rate of a two-spin correlated state (dipolar order) in addition to a state that is linear in spin operators (Zeeman order) and comparison with theoretical predictions.
An important question for many-body systems is how microscopic quantum mechanical parameters influence a corresponding dynamic at the macroscopic scale. Single crystal of calcium fluoride is an ideal test system for experimental investigation of such phenomenon-the spin degrees of freedom are well defined, relaxation times can be very long, and internal dynamics such as spin diffusion are kinematically simple. Experimentally, one can control the nuclear spin system by average Hamiltonian theory, developed by J. S. Waugh and coworkers, to study how a microscopic quantum property such as a spin state affects a macroscopic observable, such as a spin diffusion rate. A method of measuring diffusion in magnetic resonance is to encode a spatial modulation of magnetization in a sample and then measure it's attenuation over time. The difficulty in measuring spin diffusion in solid crystals by these scattering methods is that the spin diffusion rate is very slow (of an order 1 x 10^-12 cm^2/s) and hence the displacement of spin coherence is very small (approximately 1 micron per hour). The experimental challenge for probing these dynamics is that a spatial modulation of the nuclear spin magnetization must be created with a wavelength on these length scales. In this talk I will describe the method by which spin diffusion can be measured, in addition to a scheme by which the homonuclear dipolar Hamiltonian can be effectively turned-off in NMR using average Hamiltonian methods. The talk will include a discussion of the measurement of the spin diffusion rate of a two-spin correlated state (dipolar order) in addition to a state that is linear in spin operators (Zeeman order) and comparison with theoretical predictions.