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Description
Solid state systems with nontrivial topology exhibit many fascinating properties that are stable under external perturbations. A prominent example are topological insulators which are insulating in the bulk but have conducting surfaces with transport on surface states whose existence is protected by the topology of the bandstructure. Among semimetals, Weyl semimetals are topological. They are characterized by the linear Weyl dispersion of electrons with a definite chirality near certain points in the Brillouin zone. These Weyl points are sources and sinks of the topological charge.
A study of photocurrents – electrical currents generated in response to homogeneous light excitation – is an efficient method of probing the topological properties of various systems. Photocurrents are allowed in non-centrosymmetric media, and their direction is determined by the system's symmetry. In Weyl semimetals, the direction of the photocurrent reverses when switching from right-handed to left-handed excitation. The value of the photocurrent in each Weyl node is proportional to its topological charge. In the semiclassical limit, where photon energies are much smaller than the mean electron energy, the value of the helicity-dependent photocurrent is determined by fundamental constants and the light frequency. We demonstrate that the microscopic mechanisms responsible for this universal photocurrent are Berry curvature and side jumps that occur during scattering by disorder. We calculate the helicity-driven photocurrent value in chiral Weyl semimetals.
