Heterogeneous cluster size distribution of coherences in the quantum dynamics of infinite spin ½ network

CLAUDIA M. SÁNCHEZ; ANA K. CHATTAH; RODOLFO H. ACOSTA; PATRICIA R. LEVSTEIN

Angra dos Reis

Encuentro; 13th Nuclear Magnetic Resonance Users Meeting (AUREMN 2011); 2011

Associação de Usuários de Ressonância Magnética Nuclear

We study the decoherence that occurs during the evolution of dipolar coupled nuclear spin systems by using solid state Nuclear Magnetic Resonance (NMR). The decoherence processes lead to a loss of information that can be quantified through a Loschmidt echo (LE). The LEs are those generated by reverting the time evolution of a system and are experimentally implemented by changing the sign of the involved Hamiltonians. We probe the spin dynamics under the evolution of a double quantum Hamiltonian, on different spin systems: adamantane involves an infinite 1/2 spin network with only intermolecular dipolar interactions, liquid crystal 5CB in the pnematic phase, where only intramolecular dipolar interactions survive giving rise to a closed system of a finite number of spins and polycrystalline ferrocene, that presents both intra and intermolecular interactions. The distribution of the coherence orders found in adamantane does not respond to the conventional gaussian distribution introduced by Baum and Pines. In this work we show that an accurate fitting is obtained by using two gaussian functions. Furthermore detailed information on the creation of different sized clusters and their evolutions under HDQ can be obtained. The experiments were performed using a Bruker Avance II spectrometer operating at a 1H resonance frequency of 300.13 MHz at 300 K. A Markovian model in the space order of coherence vs. number of correlated spins was used to simulate the dynamics of cluster evolutions. Selection rules are incorporated to characterize the Hamiltonian and jump probabilities take into account the coupling of the network. Within the spins effectively moving in this space a leaking probability is introduced to simulate decoherence. Comparisons with experimental data shows very good agreement.