EPFL Doctorate Award 2021 - Alberto Ciarrocchi

For ground-breaking work on the realization of the first room-temperature exciton transistor and fundamental contributions to the understanding of exciton transport in two-dimensional semiconductors.

Two-dimensional (2D) crystals are a fascinating class of quantum materials with unique optical, electronic and mechanical properties. Being atomically thin, these materials offer the possibility to realize ultimately scaled down computing and sensing devices, as well as to explore very exotic physical phenomena in reduced dimensionalities.

This thesis investigates the behaviour of semiconducting 2D crystals and their heterostructures, with the aim of realizing novel computing devices based on the multiple quantum degrees of freedom (charge, spin and valley) available in these structures.

The first part of the dissertation studies the layered crystal PtSe₂ as a material for nano electronic devices with tuneable properties. We demonstrate multiple kinds of atomic-scale engineering, including a metal-semiconductor transition and a layer-dependent, defect-induced magnetism. The second part of the thesis explores logic devices based on the transport of indirect excitons in 2D heterostructures. A room temperature excitonic switch is demonstrated, as well as electric control over the polarization, energy and brightness of exciton fluxes. Building on top of these results, an excitonic switch for currents of valley-polarized excitons, i.e. a valleytronic transistor, is finally realized.