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Strong correlations in materials are facilitated through electron-electron or electron-phonon interactions and lead to phenomena beyond the single-active-electron picture of traditional solid-state physics. In the prototypical material 1T-TaS2, these interactions lead to a specific surface reconstruction at low temperatures closely linked to a charge density wave. At low temperatures, the surface of 1T-TaS2 shows a correlation band gap, while at higher temperatures the surface is metallic [1].
As the specific electronic and structural properties of this class of Peierls-Mott transition materials are defined by electron-electron and -phonon interactions, electronic excitations may weaken the surface stability and allow for transitions into different phases. Such phases, which cannot be reached in thermodynamic equilibrium, are particularly interesting for novel application for electronic devices [2].
We utilize the strong electronic interaction of highly charged ions with a surface to induce a chiral switch in the commensurate charge density wave phase at 50K of 1T-TaS2. By monitoring the evolution of the surface band structure under ion bombardment in operando with angle-resolved photoelectron spectroscopy, we observe a gradual change of the surface (2D) chirality. We explain our findings by the ion destabilizing the electronic structure of the surface upon neutralization. At the same time, introducing single atomic displacements breaks the surface symmetry, and surface atoms are rearranged in the opposite chirality upon energy dissipation [3].
Our results show that the electronic interaction of ions can be used to tailor surfaces which are governed by strong correlations. This opens the door towards the rich toolbox of ion beam physics for quantum materials.
[1] K. Rossnagel, J. Phys. Cond. Matter 26 (2011) 213001.
[2] L. Stojchevska, Science 344 (2014) 6180.
[3] A. Niggas et al., Nano Lett. 26 (2026) 2002.