Picosecond electric-field-induced threshold switching in phase-change   materials
  Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag$_4$In$_3$Sb$_{67}$Te$_{26}$. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on sub-picosecond time-scales - faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch. 
Peter Zalden, Michael J. Shu, Frank Chen, Xiaoxi Wu, Yi Zhu, Haidan   Wen, Scott Johnston, Zhi-Xun Shen, Patrick Landreman, ...
cond-mat.mtrl-sci