Nonlinear susceptibilities and polydispersivity in dipolar glasses

The dipolar glass system D-BP(40)BPI(60) was investigated using broadband dielectric spectroscopy over 12 decades in frequency and temperatures between 4 K < T< 300 K. The complex dielectric constant reveals increasing polydispersivity with decreasing temperatures. However, no criticality can be detected in the linear components of the susceptibility: the distribution of relaxation times, as well as the mean relaxation time become infinite at T=0 only. The nonlinear susceptibility was followed over 4 decades of frequency. Again the mean relaxation times follow a pure Arrhenius-type behavior. However, from the extrapolation of the quasistatic nonlinear susceptibility a glass transition temperature of 30 K can be deduced in reasonable agreement with the Almeida-Thouless line determined from measurements of the FC/ZFC-susceptibilities. 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.