Bulk photovoltaic effects in altermagnets
Motohiko Ezawa
Abstract
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><</d:mo> <d:mi>ℏ</d:mi> <d:mi>ω</d:mi> <d:mo><</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.