Electron transport in atomically thin crystals

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Abstract

This work is dedicated to electron transport in atomically thin crystals. We explorehydrodynamic effects in the electron liquid of graphene and perform a comprehensivestudy of electronic and optical properties of a novel 2D semiconductor - indium selenide(InSe).Graphene hosts a high quality electron system with weak phonon coupling such thatelectron-electron scattering can be the dominant process responsible for the establish-ment of local equilibrium of the electronic system above liquid nitrogen temperatures.Under these conditions, charge carriers are expected to behave as a viscous fluid witha hydrodynamic behaviour similar to classical gases or liquids. In this thesis, we aimedto reveal this hydrodynamic behaviour of the electron fluid by studying transport prop-erties of high-quality graphene devices. To amplify the hydrodynamic effects we useda special measurement geometry in which the current was injected into the graphenechannel and the voltage was measured at the contact nearest to the injector. In thisgeometry we detected a negative signal which is developed as a result of the viscousdrag between adjacent fluid layers, accompanied by the formation of current vortices.The magnitude of the signal allowed us to perform the first measurement of electronviscosity.In order to understand how an electron liquid enters the hydrodynamic regimewe studied electron transport in graphene point contacts. We observed a drop in thepoint contact resistance upon increasing temperature. This drop was attributed to theinteraction-induced lubrication of the point contact boundaries that was found to bestrong enough to prevent momentum relaxation of charge carriers. The viscosity of theelectron fluid was measured over a wide range of temperatures and at different carrierdensities. Experimental data was found to be in good agreement with many-bodycalculations.In this work we also studied transport properties of two-dimensional InSe. Weobserved high electron mobility transport, quantum oscillations and a fully developedquantum Hall effect. In optical studies, we revealed that due to the crystal symmetrya monolayer InSe features suppressed recombination of electron-hole pairs

Keyword(s)

2D materials; Electron transport; Graphene

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