Probing Hydrodynamic Transport in Graphene Heterostructures

Niblett, Andy and Ponomarenko, Leonid and Kolosov, Oleg (2026) Probing Hydrodynamic Transport in Graphene Heterostructures. PhD thesis, Lancaster University.

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Abstract

This thesis addresses two outstanding gaps in the study of electronic transport in graphene. The first concerns the inadequacy of conventional Drude models to describe charge transport near the neutrality point (NP). Using transport measurements on high-mobility hBN-encapsulated graphene devices, we show that electron-hole interactions near the NP produce apparent negative mobilities that were previously unexplained. In collaborative work, a drag-modified Drude model was developed that accurately reproduces measured longitudinal and Hall resistivities. This demonstrated that the negative mobility was due to significant electron-hole drag (majority-carriers drag the minority-carriers). The model provides a predictive, compact description of graphene transport over a wide range of carrier densities and a practical method for extracting microscopic scattering times from macroscopic resistivity data. The second advance is the introduction of a systematic method to analyse scanning gate microscopy (SGM) data in transport experiments. While SGM had been previously applied to probe transport in 2D materials, no experimental work, until now, had been demonstrated on spatially probing hydrodynamic transport in graphene-based devices. Further, no solid framework appears for interpreting such spatial resistance maps. Here, we establish such a framework by combining SGM measurements with analytical solutions, in simplified geometries, and in finite-element simulations. We reveal unexpected crescent-shaped response patterns in four-probe non-local configurations, characteristic of diffusive flow. Likewise, unique patterns were observed at lower temperatures, 160 K, consistent with hydrodynamic flow. Further, the numerical analysis enabled the extraction of the electronic fluid's kinematic viscosity from spatial SGM maps. Together, these studies demonstrate the significance of carrier-carrier interactions that produce measurable phenomena. Our models and insight provide a better understanding of interacting electronic fluids. The methodologies developed here supply models and experimental tools that may extend beyond graphene, offering a foundation for future studies of intrinsic transport in two-dimensional materials.