Graphene’s isolation took the world by surprise and was meant to revolutionize modern electronics. However, it was soon realized that its intrinsic properties limit the utilization in our daily electronic devices. When a concept of Mathematics, namely Topology, met the field of on-surface chemistry, new materials with exotic features were theoretically discovered. Topological materials exhibit technological relevant properties such as quantum hall conductivity that are protected by a concept similar to the comparison of a coffee mug and a donut. These structures can be synthesized by the versatile molecular engineering toolbox that surface reactions provide. Nevertheless, the realization of such a material yields access to properties that suit the figure of merits for modern electronic application and could eventually for example lead to solve the ever-increasing heat conflict in chip design. However, problems such as low crystallinity and defect rich structures prevented the experimental observation and kept it for more than a decade a playground only investigated theoretically.
An international team of scientists from Institut National de la Recherche Scientifique (Centre Energie, Matériaux et Télécommunications), McGill University and Lakehead University, both located in Canada, and the SAMOS laboratory of the Istituto di Struttura della Materia (Cnr), led by Giorgio Contini, demonstrates, in a recent publication on Nature Materials, that the synthesis of two-dimensional π-conjugated polymers with topological Dirac cone and flats bands became a reality allowing a sneak peek into the world of organic topological materials.
Complementary work of organic chemists and surface scientists lead to two-dimensional polymers on a mesoscopic scale and granted access to their electronic properties. The band structure of the topological polymer reveals both flat bands and a Dirac cone confirming the prediction of theory. The observed coexistence of both structures is of particular interest, since whereas Dirac cones yield massless charge carriers (a band velocity of the same order of magnitude of graphene has been obtained), necessary for technological applications, flat bands quench the kinetic energy of charge carriers and could give rise to intriguing phenomena such as the anomalous Hall effect, surface superconductivity or superfluid transport.
This work paths multiple new roads – both theoretical and experimental nature. The integration of this topological polymer into a device such as transistors possibly reveals immense performance. On the other hand, it will foster many researchers to explore a wide range of two-dimensional polymers with different lattice symmetries, obtaining insight into the relationship between geometrical and electrical topology, which would in return be beneficial to fine tune a-priori theoretical studies. These materials - beyond graphene - could be then used for both their intrinsic properties as well as their interplay in new heterostructure designs.
The authors are currently exploring the practical use of the realized material trying to integrate it into transistors, pushing toward a complete designing of artificial topological lattices.
This work was partially supported by a project Grande Rilevanza Italy-Quebec of the Italian Ministero degli Affari Esteri e della Cooperazione Internazionale (MAECI), Direzione Generale per la Promozione del Sistema Paese.