Bulk photovoltaic effects in altermagnets

The bulk photovoltaic effect is a photocurrent generation from alternating electric field, which is a promising candidate for future efficient solar cell technology. It is the second-order optical current, which is the injection current or the shift current. We focus on the direct current generation. By employing a simple two-band model of the $d$-wave altermagnet coupled with the Rashba interaction, we show that the linearly polarized light can generate the injection and shift currents when the N\'{e}el vector points to an in-plane direction. The magnitude of the injection current is almost constant over a wide range of the frequency $\omega$ of the applied light provided it is smaller than a certain critical frequency $\omega _{\text{c}}$ and larger than the bulk gap energy $\varepsilon _{\text{gap}}$, $\varepsilon _{\text{gap}}<\hbar \omega <\hbar \omega _{\text{c}}$. Hence, the use of the injection current is quite efficient for solar cell technology because any photon whose energy is within this range can be equally utilized.