Friday, November 02, 2007

Hiyam's Journal Update

Phys. Rev. Lett. 99, 187003 (2007)
NMR Relaxation and Resistivity from Rattling Phonons in Pyrochlore Superconductors
Thomas Dahm1,2 and Kazuo Ueda1
(Received 13 June 2007; published 30 October 2007)

We calculate the temperature dependence of the NMR relaxation rate and electrical resistivity for coupling to a local, strongly anharmonic phonon mode. We argue that the two-phonon Raman process is dominating NMR relaxation. Due to the strong anharmonicity of the phonon an unusual temperature dependence is found having a low temperature peak and becoming constant towards higher temperatures. The electrical resistivity is found to vary like T2 at low temperatures and following a behavior at high temperatures. Both results are in qualitative agreement with recent observations on -pyrochlore oxide superconductors.

Phys. Rev. Lett. 99, 187601 (2007)

Stochastic Dipolar Recoupling in Nuclear Magnetic Resonance of Solids
Robert Tycko
(Received 1 August 2007; published 2 November 2007)

I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body systems.

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