Direct optical detection of Weyl fermion chirality in a topological semimetal

5 years ago

Direct optical detection of Weyl fermion chirality in a topological semimetal

Ching-Kit Chan, Weiwei Xie, Hsin Lin, Yuxuan Lin, Nuh Gedik, Pablo Jarillo-Herrero, Shuang Jia, Guoqing Chang, Tomás Palacios, Cheng-Long Zhang, Su-Yang Xu, Qiong Ma, Patrick A. Lee

In 1929, H. Weyl discovered that all elementary fermions that have zero mass must attain a definitive chirality determined by whether the directions of spin and motion are parallel or anti-parallel¹. Such a chiral massless fermion is called the Weyl fermion (WF). Although none of the fundamental particles in high-energy physics was identified as WFs, condensed matter researchers have found an analogue of this elusive particle in a new class of topological materials, the Weyl semimetal (WSM)^{2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}. Similar to the case in high-energy physics, the WFs in a WSM also have a definitive chirality. A right-handed Weyl node (χ = +1) is a monopole (a source) of Berry curvature whereas a left-handed Weyl node (χ = −1) is an anti-monopole (a drain) of Berry curvature. Any Fermi surface enclosing a right(left)-handed Weyl node (χ = ±1) has a unit Berry flux coming out (in) and hence carries a Chern number C = ±1 (Fig. 1a). As a result, the chirality of the WF serves as its topological number.

Publisher URL: http://dx.doi.org/10.1038/nphys4146

DOI: 10.1038/nphys4146