Bulk and surface photocurrents in topological chiral crystals

The nonlinear optical responses from topological semimetals are crucial in both understanding the fundamental properties of quantum materials and designing next-generation light sensors or solar cells. Using the ideal topological chiral semimetal RhSi as a representative, we, for the first time, theoretically determine the quantized photocurrent from bulk multi-fold chiral fermions. We further propose a new surface-only photocurrent response from their chiral Fermi arcs. We quantitatively compute the photogalvanic currents from bulk "Weyl" cone and surface Fermi arcs. We demonstrate that Fermi arc photogalvanic currents can be perpendicular to the bulk injection currents regardless of the choice of materials surface. We then generalize this finding to other cubic chiral space groups and predict material candidates. Our theory reveals a powerful notion where common crystalline symmetry can be used to completely disentangle bulk and surface optical responses in many conducting material families.