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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>d</a:mi></a:math>-wave altermagnet coupled with the Rashba interaction, we show that the linearly polarized light can generate the injection and shift currents when the Néel vector points to an in-plane direction. The magnitude of the injection current is almost constant over a wide range of the frequency <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>ω</b:mi></b:math> of the applied light provided it is smaller than a certain critical frequency <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi>ω</c:mi><c:mtext>c</c:mtext></c:msub></c:math> and larger than the bulk gap energy <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:msub><d:mi>ɛ</d:mi><d:mtext>gap</d:mtext></d:msub><d:mo>,</d:mo><d:mo> </d:mo><d:mrow><d:msub><d:mi>ɛ</d:mi><d:mtext>gap</d:mtext></d:msub><d:mo>&lt;</d:mo><d:mi>ℏ</d:mi><d:mi>ω</d:mi><d:mo>&lt;</d:mo><d:mi>ℏ</d:mi><d:msub><d:mi>ω</d:mi><d:mtext>c</d:mtext></d:msub></d:mrow></d:math>. 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.