Colossal switchable photocurrents in topological Janus transition metal dichalcogenides

Jing Kong,Ju Li,Haowei Xu,Jian Zhou,Yunfan Guo,Hua Wang

doi:10.1038/s41524-021-00499-4

Jing Kong, Ju Li + Show 4 more

Open Access

https://doi.org/10.1038/s41524-021-00499-4

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Abstract

Nonlinear optical properties, such as bulk photovoltaic effects, possess great potential in energy harvesting, photodetection, rectification, etc. To enable efficient light–current conversion, materials with strong photo-responsivity are highly desirable. In this work, we predict that monolayer Janus transition metal dichalcogenides (JTMDs) in the 1T′ phase possess colossal nonlinear photoconductivity owing to their topological band mixing, strong inversion symmetry breaking, and small electronic bandgap. 1T′ JTMDs have inverted bandgaps on the order of 10 meV and are exceptionally responsive to light in the terahertz (THz) range. By first-principles calculations, we reveal that 1T′ JTMDs possess shift current (SC) conductivity as large as 2300 nm μA V−2, equivalent to a photo-responsivity of 2800 mA/W. The circular current (CC) conductivity of 1T′ JTMDs is as large as ∼104 nm μA V−2. These remarkable photo-responsivities indicate that the 1T′ JTMDs can serve as efficient photodetectors in the THz range. We also find that external stimuli such as the in-plane strain and out-of-plane electric field can induce topological phase transitions in 1T′ JTMDs and that the SC can abruptly flip their directions. The abrupt change of the nonlinear photocurrent can be used to characterize the topological transition and has potential applications in 2D optomechanics and nonlinear optoelectronics.

Highlights

With the development of strong light sources, nonlinear optical (NLO) materials have the potential to engender new physical effects
We would like to note that, in addition to nonlinear photocurrents, other NLO effects such as the secondharmonic generation are colossal in 1T′ Janus transition metal dichalcogenides (JTMDs) (Supplementary Fig. 10)
The inversion symmetry of 1T′ pristine TMDs (PTMDs) can be broken externally by, e.g., an out-of-plane electric field, resulting in nonlinear photocurrents, which can be regarded as a third-order nonlinear effect

Summary

Introduction

With the development of strong light sources, nonlinear optical (NLO) materials have the potential to engender new physical effects. The generation of nonlinear direct photocurrent upon light illumination has evoked great interest. This is known as bulk photovoltaic effect (BPVE)[1]. The photocurrent under linearly polarized light, or the shift current (SC), has been theoretically predicted and experimentally observed in materials such as multiferroic perovskites[2,3,4,5,6,7] and monolayer monochalcogenides[8,9,10]. Besides SC, the circular photogalvanic effect[12,13,14,15,16] that generates circular current (CC) (aka injection current) under circularly polarized light is another nonlinear photocurrent effect. The direction of CC can be effectively controlled by the handedness of the circularly polarized light

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Conclusion