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Despite being very weak, the chiral optical response of natural media plays a fundamental role in several areas of photonics, medicine, pharmacology, and quantum optics. Topological insulators are a class of materials in which spin-momentum locking induces a preferential response of surface electrons to circularly polarized light. However, the resulting spin-polarized photocurrents are often hindered by the strong contribution of bulk electrons. Here we show that the intrinsic circular photogalvanic effect in topological insulator BSTS (Bi1.5Sb0.5Te1.8Se1.2), probed by helicity dependent photocurrent, can be enhanced by one order of magnitude when a non-chiral metamaterial design is patterned on the crystal surface. This method can be adopted to control the polarization properties of Dirac materials beyond topological insulators by metamaterial design, opening up new opportunities for the detection of quantum light, molecular sensing, and the realization of opto-spintronic devices.
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