Figure 1

Third-order harmonic component of the dielectric susceptibility of glycerol. Spectra of $|{\chi }_3|E^2$ are shown for various temperatures, measured at a field of $565\mathrm{kV}/\mathrm{cm}$. The inset shows the hump amplitude in the quantity $X$ as determined from ${\chi }_3$ (see text), which is proportional to the number of correlated molecules $N_{\mathrm{corr}}$. The line is a guide to the eye.Reuse & Permissions

Figure 2

Third-order harmonic component of the dielectric susceptibility of PC. Spectra of $|{\chi }_3|E^2$ are shown for various temperatures measured at a field of $225\mathrm{kV}/\mathrm{cm}$. Shaded areas show the hump. Arrows indicate the peak positions in the dielectric loss [6]. The inset shows $X_{\max }\propto N_{\mathrm{corr}}$. The line is a guide to the eye.Reuse & Permissions

Figure 3

Third-order harmonic component of the dielectric susceptibility of 2E1H. Spectra of $|{\chi }_3|E^2$ are shown for various temperatures measured at a field of $460\mathrm{kV}/\mathrm{cm}$. Shaded areas show the hump. Arrows indicate the peak positions in the dielectric loss [18]. The inset shows $X_{\max }\propto N_{\mathrm{corr}}$. The line demonstrates nearly constant behavior.Reuse & Permissions

Figure 4

Correlation of apparent activation enthalpy with the number of correlated molecules. Lines: derivatives of the relaxation-time fits revealing the temperature-dependent apparent activation enthalpies (right scale). Symbols: scaled hump amplitudes of $X$, determined from ${\chi }_3$, which are proportional to the number of correlated molecules $N_{\mathrm{corr}}$ (left scale). The open circles show the results on glycerol from Ref. 15. The $N_{\mathrm{corr}}$ data points (including those from Ref. 15) were multiplied by separate factors for each material (glycerol: 1.15, PC: 0.72, FAN: 1.30, 2E1H: 0.39) leading to a good match with the derivative curves. (For FAN, two separate measurement runs were performed. The deviation of the results at given temperature provides an estimate of the error bars.) Inset: temperature-dependent relaxation times of the investigated glass formers in Arrhenius representation, taken from Refs. 30 (glycerol, PC), 16 (FAN), and 18 (2E1H). The lines are fits with the VFT function.Reuse & Permissions