Dipolar Order Controls Dielectric Response of Glass-Forming Liquids

The dielectric response of liquids reflects both reorientation of single molecular dipoles and collective modes, i.e., dipolar cross-correlations. A recent theory predicts the latter to produce an additional slow peak in the dielectric loss spectrum. Following this idea we argue that in supercooled liquids the high-frequency power law exponent of the dielectric loss $\ensuremath{\beta}$ should be correlated with the degree of dipolar order, i.e., the Kirkwood correlation factor ${g}_{\mathrm{K}}$. This notion is confirmed for 25 supercooled liquids. While our findings support recent theoretical work the results are shown to violate the earlier Kivelson-Madden theory.