Interlayer electron-hole friction in tunable twisted bilayer graphene semimetal

Charge-neutral conducting systems represent a class of materials with unusual properties governed by electron-hole (e-h) interactions. Depending on the quasiparticles' statistics, band structure, and device geometry these semimetallic phases of matter can feature unconventional responses to external fields that often defy simple interpretations in terms of single-particle physics. In this talk, we will show that small-angle twisted bilayer graphene (SA-TBG) offers a highly-tunable system in which to explore interactions-limited electron conduction. We will see that by employing a dual-gated device architecture one can tune SA-TBG devices from a non-degenerate charge-neutral Dirac fluid to a compensated two-component e-h Fermi liquid where spatially separated electrons and holes experience strong mutual friction [1]. This friction is revealed through the T² resistivity that accurately follows the e-h drag theory we developed. Our results provide a textbook illustration of a smooth transition between different interaction-limited transport regimes and clarify the conduction mechanisms in charge-neutral SA-TBG.

[1] D.A. Bandurin, et al., arXiv:2208.05659 (2022).