Zener Tunneling Breakdown in Phase-Change Materials Revealed by Intense Terahertz Pulses

We have systematically investigated the spatial and temporal dynamics of crystallization that occurs in the phase-change material Ge2Sb2Te5 upon irradiation with an intense THz pulse. THz pump and optical probe spectroscopy revealed that Zener tunneling induces a nonlinear increase in the conductivity of the crystalline phase. This result indicates that the large electric field associated with the THz pulses causes a nonlinear increase only at the edge of the crystallized area. The electric field concentrating in this area causes a temperature increase via Joule heating, which in turn leads to nanometer scale crystal growth parallel to the field and the formation of filamentary conductive domains across the sample.