J. Phys. I France 7 (1997) 977-1001
Phase Pinning by EPR Probe in Biphenyl Doped with NaphthaleneA. Veron and J. Emery
Laboratoire de Physique de l'État Condensé UPRES-A 6087, avenue Olivier Messiaen, 72085 le Mans Cedex 9, France
(Received 22 January 1997, received in final form 1 April 1997, accepted le 21 April 1997)
The naphthalene Electronic Paramagnetic Resonance probe used to study the phase transitions in biphenyl does not account for the plane wave modulation of the incommensurate phase II. Its EPR spectra yields a phase distribution which looks like a "multi-soliton regime". Moreover, the splitting between the edge singularities is not symmetrical, in contradiction with a linear one. This behaviour is not exhibited by the phenanthrene EPR probe whose spectra account well enough for the plane wave modulation with a linear coupling to the order parameter. To analyse the defect behaviour of the probe, we first introduce a coupling between the probe and the modulation wave and determine the phase distribution within the phenomenological Landau theory. Furthermore, a calculation based on intermolecular interaction is performed in order to describe the microscopic origin of this distribution and is applied to naphthalene and phenanthrene molecular probes.
© Les Editions de Physique 1997