Nonlinear susceptibilities and polydispersivity in dipolar glasses

The dipolar glass system D-BP40BPI60 was investigated using broadband diele ctric spectroscopy over 12 decades in frequency and temperatures between 4 K < T< 300 K. The complex dielectric constant reveals increasing polydisper sivity with decreasing temperatures. However, no criticality can be detecte d in the linear components of the susceptibility: the distribution of relax ation times, as well as the mean relaxation time become infinite at T=0 onl y. The nonlinear susceptibility was followed over 4 decades of frequency. A gain the mean relaxation times follow a pure Arrhenius-type behavior. Howev er, from the extrapolation of the quasistatic nonlinear susceptibility a gl ass transition temperature of 30 K can be deduced in reasonable agreement w ith the Almeida-Thouless line determined from measurements of the FC/ZFC-su sceptibilities. The frequency dependence of the real and imaginary parts of the third-order susceptibility cannot be described using simple extensions from Cole-Cole or Havriliak-Negami functions.