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ABSTRACT
The recently discovered twist-bend nematic phase, NTB, has short-pitched heliconical structure with doubly degenerate handedness. In contrast to the classic nematic, in the NTB phase the director is spontaneously distorted, resulting in unusual elastic properties. The response of the NTB phase to external stimuli, like chiral doping or applied fields might provide further information about its structure and can find utilisation in practical applications. Here, the NTB behaviour is theoretically investigated under chiral doping and strong electric fields. We show that the chiral doping removes the NTB degeneration and modifies the conical tilt angle, leaving the pitch unchanged. Thus, the NTB helical twisting power is very high and strongly non-linear. Under electric field, we consider separately the ferroelectric, flexoelectric and dielectric couplings. We show that the experiments reported so far disagree with the ferroelectric behaviour, indicating that the NTB phase is not spontaneously polarised. On the contrary, the observed polar effects fit well with the flexoelectric coupling, confirming the degenerated heliconical structure of the phase. Under very strong fields, we predict a second-order twist-bend nematic – nematic phase transition due to the dielectric torque on the director.
Graphical Abstract
Acknowledgements
I acknowledge fruitful discussions with Geoffrey G. Luckhurst, Ivan Dozov and Patrick Davidson on the field effects in the twist-bend nematic phase. This work was supported financially by the grant ANR-15-CE24-0012BESTNEMATICS of Agence Nationale de la Recherche, France.
Disclosure statement
No potential conflict of interest was reported by the author.