IFEG   20353
INSTITUTO DE FISICA ENRIQUE GAVIOLA
Unidad Ejecutora - UE
artículos
Título:
Hole burning in polycrystalline C60: An answer to the long pseudocoherent tails
Autor/es:
MARÍA BELÉN FRANZONI; PATRICIA R. LEVSTEIN; JÉSUS RAYA AND JÉRÔME HIRSCHINGER
Revista:
PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS
Editorial:
American Physical Society
Referencias:
Año: 2008 vol. 78 p. 115407 - 115411
ISSN:
0163-1829
Resumen:
NMR experiments in C60 reveal the origin of the “pseudocoherence” that leads to long tails in some Carr-Purcell-Meiboom-Gill (CPMG) sequences in contrast with the decay of a standard Hahn echo.We showed in a previous work (M. B. Franzoni and P. R. Levstein, Phys. Rev. B 72, 235410,2005) that under certain conditions these CPMG sequences become spoiled by stimulated echoes. The presence of these echoes evidences that the long tails arise on the storage of magnetization in the direction of the external magnetic field (z polarization) involving spin-lattice relaxation times of several seconds. Hole burning experiments confirm the presence of a highly inhomogeneous line and show that the flip-flop processes are able to homogenize the line in times agreeing with those obtained through a Hahn echo sequence. As expected, the decay of the stimulated echoes is not sensitive to the quenching of the dipolar interaction through an MREV16 sequence, while the Hahn echo decay increases by a factor of 20. CPMG sequences with hard pulses and different temporal windows clearly show the relevance of the dipolar interaction in between the pulses for the generation of the long tails. In particular, the more time the flip flop is effective (longer interpulse separation), the amplitudes of the long tails decrease and their characteristic times become shorter.