Main characteristic properties of incommensurate biphenyl

We underline two main characteristic properties of the incommensurate phases in biphenyl. On the one hand, the sequence of incommensurate phases is unusual, with the existence of a partial lock-in transition between a phase II with a two-dimensional modulation wave and a phase III with only a one-dimensional one. On the other hand, the specific dynamic properties of these incommensurate phases can easily be studied due to the low values of phonon damping at low temperature. The remaining incommensurability at absolute zero for the atmospheric pressure has allowed the observation of propagating phasons in phase III. Moreover, both transition temperatures tend towards the absolute zero for moderate pressure and this effect is profitable to study phasons and amplitudons in phase II under better conditions.