The influence of pressure-dependent variation of the elastic constants on tunnelling systems in amorphous solids

We have measured the dielectric response epsilon(omega) and the thermal con ductivity kappa of polystyrene (PS) and of polycarbonate (PC) under high hy drostatic pressure (0.1 MPa < p < 650 MPa) and at low temperatures (50 mK < T < 100 Kf. The investigations show a pressure influence on the minimum te mperature of AE;IE) and on ri. With the pressure dependence of the density and sound velocity of PC and PS the influence of pressure on the tunnelling constant Ci can be determined. These results show that the product (P) ove r bar gamma(1,t)(2), of the standard tunnelling model (STM) scales with the pressure-dependent elastic constants c(11) and C-44. (C) 2000 Elsevier Sci ence B.V. All rights reserved.