Many physical systems respond to slowly changing external force through avalanches spanning broad range of sizes. Some systems crackle even without apparent external force, such as bursts of neuronal activity or charge transfer avalanches in 2D molecular layers. Advanced development of theoretical models describing disorder-induced critical phenomena calls for experiments probing the dynamics upon tuneable disorder. Here we show that isomeric structural transitions in 2D organic self-assembled monolayer (SAM) exhibit critical dynamics with experimentally tuneable disorder. The system consists of field effect transistor coupled through SAM to illuminated semiconducting nanocrystals (NCs). Charges photoinduced in NCs are transferred through SAM to the transistor surface and modulate its conductivity. Avalanches of isomeric structural transitions are revealed by measuring the current noise I(t) of the transistor. Accumulated surface traps charges reduce dipole moments of the molecules, decrease their coupling, and thus decrease the critical disorder of the SAM enabling its tuning during experiments.
Bibliographical noteFunding Information:
This work has been partially supported by the Israeli Science Foundation, administered by the Israel Academy of Sciences and Humanities (grant 754/09). YP would like to thank the Peter Brojde center for innovation. Many thanks to Achim Catalina for throwing such wonderful ideas. Special thanks to Kamil Gradkowski and Uri Banin for providing the nanocrystals. KD thanks the Faculty of Natural Science of Ben Gurion University for hospitality and support through the Dozor program and NSF for support through DMR-1005209.