We theoretically study direct current generation in a quantum spin chain induced by spinon excitations by light irradiation. We consider a $S=1/2$ one-dimensional (1D) antiferromagnetic XXZ model with magnetoelectric coupling that describes multiferroics with broken inversion symmetry. We perform the real-time simulation using infinite time-evolving block decimation, and demonstrate the direct current generation under light irradiation. By comparing the second-order nonlinear conductivity and the two-spinon excitation spectra of a 1D XXZ model, we confirm that the spinon excitations are the origin for the direct current generation in the quantum spin chain. We find that the bulk photovoltaic effect is driven by electric polarization carried by the spinons through the shift current mechanism, and thus is regarded as “the spinon shift current.”

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• Photocurrent
• Shift current
• Spin liquid
• Spinon
• 1-dimensional spin chains
• Tensor network methods