INVESTIGADORES
SEGNORILE Hector Hugo
artículos
Título:
Evidence for several dipolar quasi-invariants in liquid crystals
Autor/es:
CLAUDIO J. BONIN; CECILIA E. GONZÁLEZ; HÉCTOR H. SEGNORILE; RICARDO C. ZAMAR
Revista:
JOURNAL OF CHEMICAL PHYSICS
Editorial:
AMER INST PHYSICS
Referencias:
Lugar: New York; Año: 2013 vol. 139 p. 14490701 - 14490710
ISSN:
0021-9606
Resumen:
The quasi-equilibrium states of an observed quantum system involve as many constants of motion
as the dimension of the operator basis which spans the blocks of all the degenerate eigenvalues of
the Hamiltonian that drives the system dynamics, however, the possibility of observing such quasiinvariants
in solid-like spin systems in Nuclear Magnetic Resonance (NMR) is not a strictly exact
prediction. The aim of this work is to provide experimental evidence of several quasi-invariants, in
the proton NMR of small spin clusters, like nematic liquid crystal molecules, in which the use of thermodynamic arguments is not justified.We explore the spin states prepared with the Jeener-Broekaert
pulse sequence by analyzing the time-domain signals yielded by this sequence as a function of the
preparation times, in a variety of dipolar networks, solids, and liquid crystals. We observe that the
signals can be explained with two dipolar quasi-invariants only within a range of short preparation
times, however at longer times liquid crystal signals show an echo-like behaviour whose description
requires assuming more quasi-invariants. We study the multiple quantum coherence content of such
signals on a basis orthogonal to the z-basis and see that such states involve a significant number
of correlated spins. Therefore, we show that the NMR signals within the whole preparation timescale
can only be reconstructed by assuming the occurrence of multiple quasi-invariants which we
experimentally isolate.