Tunable Weyl Points in Periodically Driven Nodal Line Semimetals

Weyl semimetals and nodal line semimetals are characterized by linear band touching at zero-dimensional points and one-dimensional lines, respectively. We predict that a circularly polarized light drives nodal line semimetals into Weyl semimetals. The Floquet Weyl points thus obtained are tunable by the incident light, which enables investigations of them in a highly controllable manner. The transition from nodal line semimetals to Weyl semimetals is accompanied by the emergence of a large and tunable anomalous Hall conductivity. Our predictions are experimentally testable by transport measurement in film samples or by pump-probe angle-resolved photoemission spectroscopy.

Figure 1

Conceptual illustration. A Dirac nodal line semimetal has band-touching lines or rings and linear dispersion in the two transverse directions. CPL lifts all the band touching except at two isolated points, near which the dispersion of the Floquet bands is linear in all three directions, i.e., Weyl points. The different colors of the Weyl cones represent different chirality ($\pm 1$).

Figure 2

The dependence of Hall conductivity on temperature ($T$), chemical potential ($\mu$), and the intensity of the incident light beam $\lambda$. The common parameters in use are $m=1$, $B=1$, $\omega =2$, $\varphi =\pi$, $v=1$, ${\epsilon }_0=0$, and we have defined the shorthand notation ${\sigma }_0=(e^2/\pi h)\sqrt{(m/B)}$. (a) ${\sigma }_{yz}$ at $\mu =0$ as a function of $\lambda$ for several values of $T$; (b) ${\sigma }_{yz}$ at $T=0$ as a function of $\lambda$ for several values of $\mu$.

Figure 3

The surface states of the NLSM and the Floquet WSM. The values of parameters are taken to be $m=B=1$, $\omega =2$, $\varphi =\pi$, $v=1$, and ${\epsilon }_0(k)=0.1(k_x^2+k_y^2)$. The chemical potential $\mu$ has been tuned to the Weyl band-touching points. (a) The shadow area ($k_x^2+k_y^2<m/B$) represents the drumhead surface states of the pristine NLSM, and the dashed lines enclose the area of surface states of the Floquet WSM ($k_x^2+k_y^2<\tilde{m}/B$), with the three colors referring to three values of $\lambda$, as indicated in the figure. The solid curves are the Fermi arcs connecting the projections of the two Weyl points onto the surface Brillouin zone. (b) The surface state dispersions of both the pristine NLSM and the Floquet WSM (with the driving parameter $\lambda =0.1$). Tilting the surface state dispersion of the NLSM leads to that of the WSM. The intersection of the dispersion of WSM and the $E=\mu$ plane is the Fermi arc.