Theory for viscous electron transport in two-dimensional electron systems*

When the quantum-mechanical carrier-carrier scattering dominates over all other scattering processes, electrons behave like a classical fluid. In this talk, I will discuss the differences in hydrodynamic transport between monolayer graphene, bilayer graphene and GaAs heterostructures. For example, I will show that hydrodynamics in bilayer graphene is more robust than in monolayer graphene, and has a characteristic “v shape” in the temperature-density plane, as opposed to a “lung shape” for monolayer graphene [1]. For unipolar hydrodynamic electrons like in GaAs heterostructures, the viscous behavior only influences the resistance through interactions with the sample boundaries, that can be modified by patterning crenellations into the sample [2]. On the other hand, for ambipolar electron fluids like bilayer graphene, we show that the electron transport decomposes into two components -- a universal Coulomb drag that dominates at charge neutrality and decays with increasing density, and a non-universal dissipative contribution corresponding to collective motion of the electron-hole plasma [3]. Finally, I will discuss the universal hydrodynamic insulator state that can be observed in ultra-clean dual-gated bilayer graphene by electrostatically opening a bandgap in an ambipolar electron fluid.

References

[1] D. Y. H. Ho, I. Yudhistira, N. Chakraborty, and S. Adam, “Theoretical determination of hydrodynamic window in monolayer and bilayer graphene from scattering rates,” Phys. Rev. B, 97, (2018), Rapid Communications.
[2] A. C. Keser et al., “Geometric control of universal hydrodynamic flow in a two-dimensional electron fluid”, Submitted (2020).
[3] C. Tan et al., “Realization of a universal hydrodynamic semiconductor in ultra-clean dual-gated bilayer graphene,” arXiv:1908.10921, Submitted (2020).