Photoinduced topological phase transition from a crossing-line nodal semimetal to a multiple-Weyl semimetal

Abstract

We propose a simple scheme to construct a model whose Fermi surface is comprised of crossing-line nodes. The Hamiltonian consists of a normal hopping term and an additional term which is odd under the mirror reflection. The line nodes appear along the mirror-invariant planes, where each line node carries the quantized Berry magnetic flux. We explicitly construct a model with the N -fold rotational symmetry, where the 2N line nodes merge at the north and south poles. Photoirradiation induces a topological phase transition. When we apply photoirradiation along the kz axis, there emerge point nodes carrying the monopole charge ±N at these poles, while all the line nodes disappear. The resultant system describes anisotropic multiple-Weyl fermions.Introduction: Weyl semimetal is one of the hottest topics in condensed matter physics 1,2 . It is protected by a monopole charge in the momentum space 3 . Multiple Weyl semimetal is a generalization of a Weyl semimetal which has a monopole charge larger than the unit charge [4][5][6][7] .There exist another class of novel semimetals. They are line nodal semimetals whose Fermi surfaces form one-dimensional lines [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . A line node is protected by a quantized Berry magnetic flux. Recently, line nodal semimetals are generalized into two species. One is a loop node forming a nontrivial link such as the Hopf link [26][27][28][29] . The other is a crossing-line node, where several line nodes cross at a point [30][31][32][33][34][35] . Photoirradiation is a powerful tool to modify the band structure [36][37][38][39][40][41] . According to the Floquet theory an additional term emerges due to the second-order process of photoirradiation. A typical example is the generation of a Weyl point from a Dirac semimetal [42][43][44][45] . It is shown that a Weyl node can also be generated by applying photoirradiation to a loop nodal semimetal 46,47 . In this paper, we first propose a simple scheme to construct models for crossing-line nodal semimetals. We then investigate how a crossing-line nodal semimetal is modified by way of photoirradiation. The model Hamiltonian consists of a normal hopping term and a mirror-odd interaction term. A line node emerges on the mirror-invariant plane. Each line node is topologically protected by the quantized Berry magnetic flux. Explicitly, we construct an N -fold rotational symmetric model, where the crossing of 2N -fold line nodes occurs at the north pole and also at the south pole. There are no magnetic monopoles at these poles. Next, we derive a photoinduced term based on the Floquet theory. It induces a topological phase transition. Indeed, by applying photoirradiation along the z direction, the Fermi surface is found to disappear by the emergence of gap except for two nodal points carrying the N (−N ) units of the monopole charge at the north (south) pole. The resultant system is the anisotropic N -fold multiple-Weyl semimetal. On the other hand, by applying photoirradiation perpendicu...

Photoinduced interfacial chiral modes in threefold topological semimetal

“…Recently, the possibility of manipulating the electronic band structure by applying a time-dependent periodic perturbation in the form of irradiation/light has received much attention, especially after the proposals of light induced topological phase transition [1][2][3][4][5][6][7][8][9][10] (the Floquet topological insulator), which has also been confirmed by experiments [11][12][13]. There is also a series of works [14][15][16][17][18] predicting phototunable Weyl nodes. Apart from these, optical pumping can also be used to control the spin and the valley degree of freedom in Dirac materials [19][20][21][22], which is the key requirement for the spin and valleytronics.…”

Floquet analysis of excitations in materials

“…For these materials especially, the high-frequency expansion of the Floquet Hamiltonian, equation (14) has proven to be very prolific, because it affords an analytic expression for the dressed Hamiltonian and as such can be readily classified in terms of topology. Thus, there have been proposals for the manipulation of Floquet-topological phases in line-node semimetals [46][47][48], Dirac-semimetals [49][50][51][52] and Weyl-semimetals [53][54][55][56][57] all relying on the effective Hamiltonian description.…”

Topological invariants of Floquet systems: General formulation, special properties, and Floquet topological defects

“…In solid-state systems, a laser beam provides a periodic driving by its timedependent electromagnetic potential A(t). Among many other interesting proposals, it has been predicted that monochromatic light can drive graphene-like Dirac bands to Floquet Chern bands 30,[39][40][41][42] , trivial insulators and semimetals to Floquet topological insulators 31,[43][44][45][46][47][48] , and nodal lines to Weyl points [49][50][51][52] or multi-Weyl points 53,54 . Experimentally, Floquet-Bloch bands have been observed at the surface of topological insulators [55][56][57] .…”