# Dresden 2020 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 21: Topological Semimetals 1

### TT 21.12: Vortrag

### Dienstag, 17. März 2020, 12:30–12:45, HSZ 103

Photoinduced Anomalous Hall Current in Nodal-Line Semimetals — •Andreas Leonhardt and Andreas P. Schnyder — Max Planck Institute for Solid State Research

Symmetry-protected nodal lines in three dimensions fall into the same topological category as graphene in two dimensions. The Berry curvature vanishes everywhere except for the nodal line, where it is divergent. This implies that the nodal line gives rise to an anomalous Hall conductivity. Like in the graphene case however, there are two valley currents from opposite sides of the nodal line that cancel exactly due to additional spatial symmetries. In candidate materials with a nodal line, spin-orbit coupling is non-negligible. Coupling the spin sub-spaces allows for the nodal line to gap out, turning the material into a topological insulator with a vanishing Berry curvature.

Driving the systems coherently with circular polarized light creates an imbalance between the two valley contributions. Using Floquet theory, we show that a net anomalous Hall current arises in the periodically driven nodal-loop semimetal. Depending on the polarization, the sign of the current can be switched, which is the distinguishing feature of this effect. We further investigate its stability upon gapping the nodal line via spin-orbit coupling or small symmetry breaking terms.