TOP WSF · Tailoring topological properties in Weyl semimetal thin films

Tailoring topological properties in Weyl semimetal thin films

In the quest for new quantum materials for electronics and energy, the investigation of topological states of matter has become a priority towards the realization of new quantum devices with unprecedented functionalities. Recently discovered Weyl semimetals attracted an incredible interest in the scientific community. Weyl semimetals are condensed matter systems in which relativistic Weyl fermions are found to exist in the form of quasiparticle excitations in correspondence of specific locations in the electronic band structure, called Weyl points. If a Weyl point is positioned close enough to the Fermi level, the transport properties of a Weyl semimetals can be dominated by the Weyl fermions instead of standard electrons, leading to exotic physical effects of both fundamental and technological interest. The uniqueness of Weyl semimetals, which make them so promising for applications, is their stability against external perturbations since the Weyl points are topologically protected and not protected by the system symmetries. This means that they could represent a robust platform for future quantum devices if we understand how to handle their properties. In order to convert promising theoretical predictions into a concrete technological perspective, trigger and tune the exceptional properties associated to non-trivial topology at the micro- and nano-scale represents a fundamental step. In this regard, the establishment of methods to fabricate high quality thin films, exfoliated flakes and micro-structured bulk samples becomes a priority. In this context, TOP-WSF aimed to explore the evolution of the transport properties of selected Weyl semimetals when their dimensions are reduced to micro and nano-structures. To reach the goal, three sub-objectives have been established: • ralization of nanostructures in form of thin films of selected topological semimetals through the pulsed laser deposition (PLD) technique; • fabrication of devices based on Weyl semimetals nanostructures for the characterization of electric and thermoelectric transport properties down to the micro and nano-scale by optical lithography, thermal scan lithography and focused ion beam (FIB) techniques; • investigation of the transport properties of the selected Wel semimetals through the fabricated devices, by tuning different parameters: temperature, magnetic field, uniaxial strain, sample dimensionality and geometry. In two years, TOP-WSF investigated several classes of Weyl semimetals, selected for different peculiar characteristics, each with a specific interest in the field of quantum technologies. The project contributed to the understanding of their electronic properties and the evaluation of their potential when the geometrical sizes are reduced to the micro- and nano-scale.

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