Out-of-equilibrium criticalities in graphene superlattices

Berdyugin, Alexey I. and Xin, Na and Gao, Haoyang and Slizovskiy, Sergey and Dong, Zhiyu and Bhattacharjee, Shubhadeep and Kumaravadivel, P. and Xu, Shuigang and Ponomarenko, L. A. and Holwill, Matthew and Bandurin, D. A. and Kim, Minsoo and Cao, Yang and Greenaway, M. T. and Novoselov, K. S. and Grigorieva, I. V. and Watanabe, K. and Taniguchi, T. and Fal’ko, V. I. and Levitov, L. S. and Kumar, Roshan Krishna and Geim, A. K. (2022) Out-of-equilibrium criticalities in graphene superlattices. Science, 375 (6579). pp. 430-433. ISSN 0036-8075

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Abstract

In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy, whereas the filled bands underneath contribute little to conduction. Here, we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics that resemble those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common to all graphene-based superlattices.