Quantum Low Dimensional Materials and their Topological and Collective Properties

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Quantum Materials allow us to explore a fascinating world of complex processes. The material acts as a host to various particles or quasi particles and defines the properties of the particles and their rules of interactions. For instance, in single layer graphene, in addition to being confined in two dimensions, electrons and phonons have special properties, where the low energy electrons have a peculiar linear dispersion (Dirac fermions) and where electronic excitations in a magnetic field can have fractional charges and unconventional statistics. Phonons in graphene are also very special. They are responsible for the very high thermal conductivity of graphene and some researchers have argued that this is related to the hydrodynamic transport of phonons (electrons show similar behavior too). For phonons this is related to the second sound of collective excitations. Many of these interesting properties are a consequence of the two-dimensional nature of the host material, where graphene is usually thought of as planar, but it is possible to curve graphene and even change its geometric topology like by forming a Möbius ring out of a single graphene layer. How would this new geometry of the local host environment impact the properties of particles like electrons and phonons or even spins? In this research program we will focus on the different interactions in these low-dimensional systems and their interplay with topology and disorder.  In particular, we will also explore in more detail the field of phonon engineering in graphene. Having arguably opened experimentally this new field of research by recently synthesizing the first isotope superlattices in graphene, we are now well positioned to explore this new Universe. The underlying idea is based on creating artificial isotope structures by controlling the position of the Carbon 13 and Carbon 12 atoms during the synthesis of graphene crystals. This is achieved by using the corresponding isotopic pure methane gases in the chemical vapor deposition of graphene. Using this technique, we were able to synthesize isotope superlattices with periods down to 6nm, which show a new graphene phonon dispersion with striking new features in the Raman spectrum. This has interesting potential applications due to the reduced thermal conductivity, which should lead to a very high Seebeck coefficient and a high figure of merit for thermoelectric applications. Part of this research program, is to measure these transport properties as a function of isotope periodicity. On the instrumentation side, we will apply super-resolution techniques to high spatial resolution imaging of chemical species via Raman spectroscopy, which will push this technique to new unexplored regime to open new pathways for advanced material characterizations.