Thursday april the 10th :
Topological semimetals are materials having symmetry-protected band crossings at either points (Dirac and Weyl semimetals), or along lines or loops (Dirac Nodal Line semimetal) in the reciprocal space. In the last case, the presence of Dirac nodal lines (DNLs) in a system makes it a good candidate for high-frequency electronic applications due to the possible high-velocity charges carriers arising from the linear band dispersion [1]. In addition, their higher density of states near the DNLs compared to Dirac semimetals would make them superior for electronic applications.
However, if calculations have predicted the existence of DNLS in a growing number of systems these last years, the experimental realizations are still sparse, especially for 2D layers [2].
In this seminar, we will concentrate more specifically on Si/Cu and Ge/Cu 2D systems. Although studied for decades, essentially from the point of view of growth mode and surface alloy formation [3], these systems have recently regained interest due to the prediction of DNLS in Cu 2 Si or Cu 2 Ge 2D crystals. We will show how, by combining angle-resolved photoemission, scanning tunnelling microscopy and DFT calculation we could evidence the existence of linearly dispersing bands and DNLs in these layers [4]. The effect of the 2D layer / substrate interaction and spin-orbit coupling will be also addressed [5].
[1] A.D. Franklin, Science, 349, 6249 (2015)
[2] B. Feng et al., Nat. Commun. 8 1007 (2017)
[3] See for example : F. Ringeisen et al., J. Vac. Science & Techn. B 1, 546 (1983) and R. Dudde et al.,
Phys. Rev. B 41, 12 029 (1990)
[4] M. Cameau et al., 2D Mater. 11 035023 (2024)
[5] M. Cameau et al., Phys. Rev. Materials 3, 4, 044004 (2019)