Abstract
The circular photogalvanic effect (CPGE) is the photocurrent generated in an optically active material in response to an applied AC electric field, and it changes sign depending on the chirality of the incident circularly polarized light. It is a non-linear DC current as it is second order in the applied electric field, and for a certain range of low frequencies, takes on a quantized value proportional to the topological charge for a system which is a source of non-zero Berry flux. We show that for a non-interacting double-Weyl node, the CPGE is proportional to two quanta of Berry flux. On examining the effect of short-ranged Hubbard interactions up to first-order corrections, we find that this quantization is destroyed. This implies that unlike the quantum Hall effect in gapped phases or the chiral anomaly in field theories, the quantization of the CPGE in topological semimetals is not protected.
Highlights
Semimetals are materials which can support gapless quasiparticle excitations in two or three dimensions, in the vicinity of isolated band touching points in the Brillouin zone, possessing discrete Fermi points. They come in different varieties, for example, the Fermi points may appear at linear band crossings, or at quadratic band crossings [1,2] (e.g., Luttinger semimetals)
We focus on the 3d double-Weyl semimetals [2,8,9], which, in the momentum space, have double the monopole charge of Weyl semimetals
The circular photogalvanic effect (CPGE) refers to the DC current that is generated as a result of shining circularly polarized light on the surface of an optically active metal [11,12,13,14]
Summary
Semimetals are materials which can support gapless quasiparticle excitations in two or three dimensions, in the vicinity of isolated band touching points in the Brillouin zone, possessing discrete Fermi points (rather than Fermi surfaces). A more non-trivial example of such semimetal is the double-Weyl semimetal, which consists of two bands touching each other linearly along one momentum direction, but quadratically along the remaining directions [3,4,5,6,7]. The CPGE refers to the part of the photocurrent that switches sign with the sign of the helicity of the incident polarized light This is a non-linear response, as it is second order in the applied AC electric field, and at low frequencies, it depends on the orbital Berry phase of the Bloch electrons. We will examine the effect of Hubbard interactions on this quantized value
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