Merging of momentum-space monopoles by controlling magnetic field: From cubic-Dirac to triple-Weyl fermion systems

摘要

We analyze a generalized Dirac system, where the dispersion along the $k_{x}$and $k_{y}$ axes is $N$-th power and linear along the $k_{z}$ axis. When weapply magnetic field, there emerge $N$ monopole-antimonopole pairs beyond acertain critical field in general. As the direction of the magnetic field isrotated toward the $z$ axis, monopoles move to the north pole whileantimonopoles move to the south pole. When the magnetic field becomes parallelto the $z$ axis, they merge into one monopole or one antimonopole whosemonopole charge is $\pm N$. The resultant system is a multiple-Weyl semimetal.Characteristic properties of such a system are that the anomalous Hall effectand the chiral anomaly are enhanced by $N$ times and that $N$ Fermi arcsappear. These phenomena will be observed experimentally in the cubic-Dirac andtriple-Weyl fermion systems ($N=3$).