Discovery of new fermions in topological chiral crystals
An object is defined as being chiral if it cannot be superimposed by its mirror image. A very familiar example is the human hand. No-matter how one orients one’s hands, it is impossible to superimpose their major features. Such a chiral asymmetry is highly important in several branches of science, ranging from molecular chemistry to biology to physics. Recently, chirality has become a hot topic in condensed matter physics through the field of topology.
In the solid state the atoms of a chiral material follow an imaginary spiral staircase like pattern. While the staircase rotates clockwise in one system, it runs counter-clockwise in the counterpart system. However, these systems, termed “enantiomers”, are mirror images of one another. The Max Planck Institute for Chemical Physics of Solids (MPI CPfS), in Dresden, Germany, is recognized world-wide as a unique source of high quality single crystals for research into quantum applications and beyond. High quality single crystals are critical to studies of many quantum properties. In recent investigations[1,2] scientists from Claudia Felser’s group at the MPI CPfS, in collaboration with M. Zahid Hasan’s team from Princeton  and Niels Schroeter from PSI together with Yulin Chen’s team from Oxford , have investigated novel topological surface states that emerge as a consequence of the structural chirality in a particular class of chiral materials that have a P213 (198) space group (SG). The researchers have discovered a new kind of quasiparticle, the so-called Rarita-Schwinger fermions, in chiral crystals, which go beyond the known Dirac and Weyl fermions.
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 D. S. Sanchez et al., Nature 567, 500 (2019).
 N. B. M. Schröter et al., Nature Physics 15 (2019).