The Pikin-Indenbom Order Parameter

A group theoretical symmetry analysis by Indenbom and his collaborators in Moscow [197,198] led, around 1977, to the introduction of a very attractive order parameter for the A -C transition which usually is referred to as the Pikin-Indenbom order parameter. It is attractive because it presents, in the simplest form possible, the correct symmetry and a very lucid connection to the secondary order parameter P. It was adopted by the Ljubljana group around Blinc for the description of both static and dynamic properties of the C phase [199-204]. The basic formalism has been described in particular detail by Pikin [40] and by Pikin and Osipov [41]. 

Py i) using the Pikin-Indenbom order parameter. The v q0" term is the higher invariant -v ( i + 2) 6 - 4 which... 

We would like to close this section with some remarks, in particular concerning the different order parameters. First of all we note a surprising thing about the very smart Pikin-Indenbom order parameter. It has been very important in the basic symmetry discussion, but it has never really been used as such in practice. Perhaps because it is too sophisticated in its simplicity. Everybody instead uses the tilt vector as order parameter. But = 1 2) is non-chiral, hence... 

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