Switchable magnetic bulk photovoltaic effect in the two-dimensional magnet CrI3

Abstract

The bulk photovoltaic effect (BPVE) rectifies light into the dc current in a single-phase material and attracts the interest to design high-efficiency solar cells beyond the pn junction paradigm. Because it is a hot electron effect, the BPVE surpasses the thermodynamic Shockley–Queisser limit to generate above-band-gap photovoltage. While the guiding principle for BPVE materials is to break the crystal centrosymmetry, here we propose a magnetic photogalvanic effect (MPGE) that introduces the magnetism as a key ingredient and induces a giant BPVE. The MPGE emerges from the magnetism-induced asymmetry of the carrier velocity in the band structure. We demonstrate the MPGE in a layered magnetic insulator CrI 3 , with much larger photoconductivity than any previously reported results. The photocurrent can be reversed and switched by controllable magnetic transitions. Our work paves a pathway to search for magnetic photovoltaic materials and to design switchable devices combining magnetic, electronic, and optical functionalities.

Valence band electronic structure of the van der Waals ferromagnetic insulators: VI$$_3$$ and CrI$$_3$$

“…Here, we point out that the recent theoretical studies have demonstrated that AFM ordering in a bilayer CrI breaks both time-reversal ( T ) and inversion ( P ) symmetries, leading to a giant nonreciprocal second-harmonic generation 35 and a magnetic photogalvanic effect 36 . In the underlying crystallographic structure, the inversion symmetry is preserved, but the AF ordering of the two FM layers within a bilayer breaks it, eliminating the need for the non-centrosymmetric crystal.…”

“…The future experimental studies of the electronic structure of thin flakes or films would offer a better insight into the development of dimensionality in these materials. Also, this would allow to study some truly exotic phenomena, predicted to occur at some thicknesses, including a giant nonreciprocal second-harmonic generation 35 and the creation of dc current by a linearly polarised light 36 in an AFM bilayer of CrI .…”

“…Furthermore, some truly remarkable phenomena have been recently investigated in the CrI bilayer where the AFM coupling between the two FM layers simultaneously breaks both the time-reversal ( T ) and the inversion ( P ) symmetries in an otherwise centrosymmetric crystal. This symmetry breaking leads to a giant nonreciprocal second-harmonic generation 35 and a magnetic photogalvanic effect 36 , or creation of dc current by a linearly polarised light, making these materials promising candidates for the future applications in which the coupling between the magnetic, optical and electronic degrees of freedom can be utilized to manipulate the properties. Also, heterostructures involving the vdW ferromagnets and superconductors could result in the elusive spin triplet superconductivity and could serve as extremely effective spin valves 37 .…”

Consequences of time-reversal-symmetry breaking in the light-matter interaction: Berry curvature, quantum metric, and diabatic motion

“…This distinction is lost in compounds which break T , as pointed out by Ref. [21] very recently, where both shift and injection current might arise for either linear or circular polarized light. While the nonlinear currents created by the incident light usually lead to Joule heating in the sample, it is possible in experiment to subtract this effect.…”

“…Thus far, research on BPVE focuses on nonmagnetic materials. However, recent theoretical [21] and experimental [22][23][24] works on magnetic systems reveal a distinct photocurrent and second harmonic generation which cannot be merely derived from the Berry phase. Therefore, we are motivated to reexamine the second-order response theory and investigate the effects of time-reversal-symmetry (T ) breaking.…”