# Observation and control of maximal Chern numbers in a chiral topological semimetal

## TL;DR

This paper demonstrates that the chiral topological semimetal PdGa exhibits maximal Chern numbers of 4, with surface Fermi-arcs and controllable topological properties via crystal handedness.

## Contribution

It provides experimental evidence of maximal Chern numbers in a chiral topological semimetal and shows control of their sign through crystal handedness.

## Key findings

- PdGa has multifold band crossings with Chern number magnitude 4.
- Reversal of Fermi-arc velocities between enantiomers.
- Handedness controls the sign of the Chern numbers.

## Abstract

Topological semimetals feature protected nodal band degeneracies characterized by a topological invariant known as the Chern number (C). Nodal band crossings with linear dispersion are expected to have at most |C|=4, which sets an upper limit to the magnitude of many topological phenomena in these materials. Here we show that the chiral crystal PdGa displays multifold band crossings, which are connected by exactly four surface Fermi-arcs, thus proving that they carry the maximal Chern number magnitude of 4. By comparing two enantiomers, we observe a reversal of their Fermi-arc velocities, which demonstrates that the handedness of chiral crystals can be used to control the sign of their Chern numbers.

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Source: https://tomesphere.com/paper/1907.08723