Direct electrical modulation of second-order optical susceptibility via phase transitions

Electrical modulation of nonlinear optical signals is crucial for emerging applications in communications and photonic circuits. However, current methods of modulating the second-order optical susceptibility involve indirectly and inefficiently changing the third-order susceptibility. Here we show that electrical switching of the crystal structure of monolayer molybdenum ditelluride can be used to directly modulate the second-order susceptibility. This approach leads to modulation of the second-harmonic generation with an on/off ratio of 1,000 and modulation strength of 30,000% per volt, as well as broadband operation of 300 nm. We also show that molybdenum ditelluride bilayers exhibit opposite modulation trends due to electrically induced heterostructures.