Ultrahigh Nonlinear Responses from MXene Plasmons in the Short-Wave Infrared Range

Abstract

Surface plasmons in 2D materials such as graphene exhibit exceptional field confinement. However, the low electron density of majority of 2D materials, which are semiconductors or semimetals, has limited their plasmons to mid-wave or long-wave infrared regime. This study demonstrates that a 2D Ti3C2Tx MXene with high electron density can not only support strong plasmon confinement with an acoustic plasmon mode in the short-wave infrared region, but also provide ultrahigh nonlinear responses. The acoustic MXene plasmons (AMPs) in the MXene (Ti3C2Tx)-insulator (SiO2)-metal (Au) nanostructure generate in the 1.5-6.0 mu m wavelength range, exhibiting a two orders of magnitude reduction in wavelength compared to wavelength in free space. Furthermore, AMP resonators with patterned Au rods exhibit a record-high nonlinear absorption coefficient of 1.37 x 10-2 m W-1 at wavelength of 1.56 mu m, approximate to 3 orders of magnitude greater than the highest value recorded for other 2D materials. These results indicate that MXenes can overcome fundamental plasmon wavelength limitations of previously studied 2D materials, providing groundbreaking opportunities in nonlinear optical applications, including all-optical processing and ultrafast optical switching. This study presents an important discovery regarding the optical properties of MXenes, demonstrating that 2D Ti3C2Tx generates a strong plasmonic phenomenon in the short-wavelength infrared range through acoustic plasmon modes. Additionally, this finding is leveraged to achieve record-high nonlinear absorption coefficients at short-wavelength infrared wavelengths. image