209 research outputs found
A neutron diffraction study of macroscopically entangled proton states in the high temperature phase of the KHCO3 crystal at 340 K
No full textInternational audienceWe utilize single-crystal neutron diffraction to study the structure of potassium hydrogen carbonate (KHCO) and macroscopic quantum entanglement above the phase transition at K. Whereas split atom sites could be due to disorder, the diffraction pattern at 340 K evidences macroscopic proton states identical to those previously observed below by F. Fillaux et al., (2006 \textit{J. Phys.: Condens. Matter} \textbf{18} 3229). We propose a theoretical framework for decoherence-free proton states and the calculated differential cross-section accords with observations. The structural transition occurs from one ordered structure () to another ordered structure. There is no breakdown of the quantum regime. It is suggested that the crystal is a macroscopic quantum object which can be represented by a state vector. Raman spectroscopy and quasi-elastic neutron scattering suggest that the state vector is a superposition of the state vectors for two -like structures symmetric with respect to planes
Methyl group tunnelling studies in calixarenes
No full textInelastic neutron scattering has been used to study the tunnelling of methyl groups belonging to several guest molecules (toluene, p-xylene, gamma-picoline) incarcerated in a host calixarene matrix. In all the cases investigated, the low tunnel-split librational states of the guest methyl groups. The main line occurs near 0.63 meV, very close to the CH3 quantum free rotor limit. In the toluence complex, the quantum regime persists at least up to 60 K. Effects of coupling between rotational and vibrational modes are discussed. Very subtle structural changes not revealed by diffraction measurements are suggested by the neutron spectroscopy results
Molecular Tunnelling in p-tert-butylcalix[4]arene(2:1)p-xylene
No full textInelastic neutron scattering has been used to study molecular tunnelling in the p-tert-butylcalix[4]arene(2:1)p-xylene complex. At low temperature the measured spectra show several bands between 0.63 and 2.6 meV which are interpreted as being due to transitions between tunnel-split librational states of the p-xylene methyl groups. Effects of coupling between a CH3 group and the whole p-xylene molecule have been observed. The rotational barrier provided by the host lattice is very small and the methyl groups behave as almost free quantum rotors
A new class of compounds suited to study the torsional dynamics in the quantum regime: the calixarenes
No full textInelastic neutron scattering spectroscopy has been used to study the rotational dynamics of methyl groups in the p-tert butylcalix [4] arene(1:1)toluene complex. The neutron scattering function shows several lines between 0. 16 and 2.6 meV, and can be satisfactorily reproduced by the single-particle model for rotational tunneling only if the presence of inequivalent sites is assumed, in contrast with the crystallographic determinations. An approach consistent with the room-temperature crystal structure and giving a satisfactory description of the experimental results is obtained by the quantum sine-Gordon model, which describes the dynamics of infinite chains of coupled methyl groups
A new look at nonlinear dynamics in solids with inelastic neutron scattering spectroscopy
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