Large Optical Nonlinearity in 1D and 2D Cuprates Investigated by Third Harmonic Generation Spectroscopy

Spectra of third-order nonlinear susceptibility |X (3) | have been investigated for 1D Mott insulators (Mls), Sr 2 CuO 3 and Ca 2 CuO 3 and 2D Mls, Nd 2 CuO 4 and La 2 CuO 4 , by using third-harmonic generation (THG) spectroscopy. The three-photon resonance to the odd-charge-transfer (CT) state enhances |X (3) |. The maximum values of |X (3) | in the 2D MIs (∼10 -10 esu) are one order smaller than those in the 1D Mls(∼10 -9 esu). The difference of the magnitudes and spectral shapes of |X (3) | between the 1D and 2D Mls can be explained by taking account of the concept of spin-charge separation.