# gst: apropos of 'strange states', the modulation of PdGa crystals from conventional to 'exotic' behaviors

<< In topological materials, electrons can display behavior that is fundamentally different from that in 'conventional' matter, and the magnitude of many such 'exotic' phenomena is directly proportional to an entity known as the Chern number. New experiments establish for the first time that the theoretically predicted maximum Chern number can be reached—and controlled—in a real material. >>

<<  in the topological semimetal palladium gallium (PdGa) one of the most common classifiers of topological phenomena, the Chern number, can reach the maximum value that is allowed in any metallic crystal. That this is possible in a real material has never been shown before. (..)  the team has established ways to control the sign of the Chern number, which might bring new opportunities for exploring, and exploiting, topological phenomena. >>

Cherned up to the maximum. Paul Scherrer Institute. Jul 9, 2020.

https://phys.org/news/2020-07-cherned-maximum.html   

<< Here, (AA) show that the chiral crystal palladium gallium (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, (They) 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. >>

Niels B. M. Schroter, Samuel Stolz, et al. Observation and control of maximal Chern numbers in a chiral topological semimetal.  Science. Vol. 369, Issue 6500, pp. 179-183. doi: 10.1126/ science.aaz3480. Jul 10, 2020.

https://science.sciencemag.org/content/369/6500/179    

Also

D.J. Thouless, F. D.M. Haldane, J. M.Kosterlitz  << opened the door on an unknown world where matter can assume strange states. >> Oct 4, 2016

https://www.nobelprize.org/prizes/physics/2016/press-release/