Theoretical and Computational Nanoscience

Main Research Lines

• Theoretical research on quantum transport phenomena in topological quantum matter (topological insulators, Weyl semimetals) in equilibrium and non-equilibrium regimes

• Spin dynamics and entanglement properties in Dirac matter (graphene, two-dimensional materials) and van der Waals heterostructures, with the search for new paradigm of quantum information manipulation

• Artificial Intelligence and machine learning techniques to accelerate the building of realistic and adaptative structural and electronic models of highly disordered materials and heterostructures

• Predictive modelling and multiscale numerical simulation of complex nanomaterials and quantum nanodevices

• Molecular dynamics, thermal transport properties and thermoelectricity in nanomaterials of interest for microelectronics (amorphous graphene and boron nitride)

In 2022 the group published the following relevant works:

Two-dimensional materials prospects for non-volatile spintronic memories

After more than a decade leading the European task force in 2D materials-based spintronics, Prof. Roche has coordinated a major overview of the state-of-the-art of the field and of the challenges currently faced in the development of non-volatile memories in general and, specifically, of those employing spintronic mechanisms such as spin-transfer torque (STT) and spin-orbit torque (SOT). Collaborating with Graphene Flagship’s partners CNRS, CEA and Thales (France) and imec (Belgium), researchers at the National University of Singapore, as well as industrial partners at Samsung Electronics (South Korea) and Global Foundries (Singapore), an in-depth discussion about the advantages of the co-integration of 2D materials in these technologies has been provided, giving a panoramic of the improvements already achieved as well as a prospect of the many advances that further research can produce, in particular in SOT-RAMs. A possible timeline of progress during the next decade is also traced.

Electrical control of spin-polarized topological currents in monolayer WTe₂

In this work, the TCN group and collaborators have demonstrated the possibility for fully coherent electrical manipulation of the spin orientation of topologically protected edge states in a low-symmetry quantum spin Hall insulator. By using a combination of ab initio simulations, symmetry-based modelling, and large-scale calculations of the spin Hall conductivity performed using in-house LSQUANT (www.lsquant.org), it is shown that small electric fields can efficiently vary the spin textures of edge currents in monolayer 1T’-WTe₂ by up to a 90-degree spin rotation, without jeopardizing their topological character. These findings suggest a new kind of gate-controllable spin-based device, topologically protected against disorder and of relevance for the development of topological spintronics.

Unveiling the multiradical character of the biphenylene network and its anisotropic charge transport

Recent progress in the on-surface synthesis and characterization of nanomaterials is facilitating the realization of new carbon allotropes, such as nanoporous graphenes, graphynes, and 2D π-conjugated polymers, following experimental pioneering work at ICN2. One of the latest examples is the biphenylene network (BPN), which was recently fabricated on gold and characterized with atomic precision. This gapless 2D organic material presents uncommon metallic conduction, which could help develop innovative carbon-based electronics. Using first principles calculations and quantum transport simulations, the TCN group has provided new insights into some fundamental properties of BPN, which are key for its further technological exploitation. We predict that BPN hosts an unprecedented spin-polarized multiradical ground state, which has important implications for the chemical reactivity of the 2D material under practical use conditions.

Toward optimized charge transport in multilayer reduced graphene oxides

In the context of graphene-based composite applications, a complete understanding of charge conduction in multilayer reduced graphene oxides (rGO) is highly desirable. However, these rGO compounds are characterized by multiple and different sources of disorder depending on the chemical method used for their synthesis. Most importantly, the precise role of interlayer interaction in promoting or jeopardizing electronic flow remains unclear. Thanks to the development of a multiscale computational approach combining first-principles calculations with large-scale transport simulations, the TCN group and co-workers have discovered interesting transport scaling laws in multilayer rGO, explaining why diffusion worsens with increasing film thickness. In contrast, contacted films are found to exhibit an opposite trend when the mean free path becomes shorter than the channel length, since conduction becomes predominantly driven by interlayer hopping. These predictions are favourably compared with experimental data and open a road toward the optimization of graphene-based composites with improved electrical conduction.