Tensor properties of the anharmonic oscillator model. Starting from Eq. (1.4.52), relevant to a collection of isotropic, centrosymmetric, anharmonic oscillators, show that the nonlinear susceptibility possesses the
with all other elements vanishing. Give a simple physical argument that explains why the vanishing elements do vanish. Also, give a simple physical argument that explains why χijhl possesses off-diagonal tensor components, even though the medium is isotropic.
