Electrical and thermoelectric transport in mixed-dimensional graphitic mesoscopic systems

Abstract

Confining electrons to fewer than three spatial dimensions increases the relative strength of potential to kinetic energy, which can generate a wide variety of novel emergent quantum phenomena. I will discuss three experiments probing the unique physics of coupled 1D-2D and 0D-2D systems. First, we studied Coulomb drag between a 1D conductor and a 2D conductor: an individual single-walled carbon nanotube and monolayer graphene, separated by a few-atom-thick hexagonal boron nitride layer. We found novel temperature- and carrier density-dependent drag behavior arising from the mixed-dimensional nature of the system, including possible hydrodynamic flow of graphene electrons generated by current in the nanotube. Separately, we measured thermal transport in carbon nanotubes using 2D graphene sections as heaters and thermometers via Johnson noise measurements. We demonstrated the high sensitivity of our thermometry technique and observed signatures of unusual energy transport due to collective 1D electronic motion combined with long-range interactions. Finally, we studied electrical and thermoelectric transport through an etch-defined graphene quantum dot in a strong magnetic field, where irregularity on the edge of a small flake in the lowest Landau level is predicted to generate novel non-Fermi liquid behavior. We found significant deviations of the thermoelectric response from the predictions of the Mott formula at high magnetic fields, and electrical conductance and thermopower resonances that suggest an interplay of quantum Hall physics, Coulomb interaction, quantum confinement and disorder at a range of temperatures.