Definition of Nematic Order

In deriving a macroscopic order parameter, we will use the diamagnetic susceptibility as an example. However, any other macroscopic property, e.g., refractive index or dielectric response, could be used as well. 

Consider the relationship between magnetic moment M and magnetic field H 

Notice that values between 0 (isotropic phase) and 1 (per- 

One might wonder if there is any relationship between Q p and P2 (cos 6) , Indeed, in nematic phases whose constituent molecules can he approximated hy simple rigid rods, these two measures of the long range order are related. The next section deals explicitly with this relationship. 

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