Electrical tunability of terahertz nonlinearity in graphene

TL;DR

This paper demonstrates that the THz nonlinearity of graphene can be effectively controlled via electrical gating, significantly enhancing its potential for ultrahigh-frequency electronic applications.

Contribution

It introduces a method to electrically tune graphene's THz nonlinearity, enabling practical, high-efficiency nonlinear devices at room temperature.

Findings

Electrical gating enhances third-harmonic generation efficiency by about two orders of magnitude.

Gating control is effective for both ultrashort and multi-cycle THz signals.

Experimental results align with a physical model of graphene nonlinearity.

Abstract

Graphene is conceivably the most nonlinear optoelectronic material. Its nonlinear optical coefficients in the terahertz (THz) frequency range surpass those of other materials by many orders of magnitude. This, in particular, allows one to use graphene for extremely efficient up-conversion of sub-THz electronic input signals into the THz frequency range at room temperature and under ambient conditions, thus paving the way for practical graphene-based ultrahigh-frequency electronic technology. Here, we show that the THz nonlinearity of graphene can be efficiently controlled using electrical gating, with gating voltages as low as a few volts. For example, optimal electrical gating enhances the power conversion efficiency in THz third-harmonic generation in graphene by about two orders of magnitude. This essentially converts graphene from an almost perfectly linear, inert electronic material to a material with the highest possible THz nonlinearity. We demonstrate gating control of THz nonlinearity of graphene for both ultrashort single-cycle and quasi-monochromatic multi-cycle input signals. Our experimental results are in quantitative agreement with a physical model of graphene nonlinearity, describing the time-dependent thermodynamic balance maintained within the electronic population of graphene during interaction with ultrafast electric fields. Our results can serve as a basis for straightforward and accurate design of devices and applications for efficient electronic signal processing in graphene at ultra-high frequencies.