Study of electron emission from 1D nanomaterials under super high field
Photoemission driven by a strong electric field of near-infrared or visible light, referred to as strong-field photoemission, produces attosecond electron pulses that are synchronized to the waveform of the incident light, and this principle lies at the heart of current attosecond technologies. However, full access to strong-field photoemission regimes at near-infrared wavelengths based on solid-state materials is restricted by space-charge screening and material damage at high optical-field strengths, which significantly hampers the realization of predicted attosecond technologies, such as ultra-sensitive optical phase modulation. Here, we demonstrate a new type of strong-field photoemission behaviour with extreme nonlinearity -- photoemission current scales follow a 40th power law of the optical-field strength, making use of sub-nanometric carbon nanotubes and 800 nm pulses. As a result, the total photoemission current depends on the carrier-envelope phase with a greatly improved photoemission current modulation depth of up to 100%, which has not previously been achieved. Time-dependent density functional calculations reveal the completely new behaviour of the optical-field induced tunnelling emission process directly from the valence band of the carbon nanotubes, which is an indication of full access to a strong-field photoemission regime. Furthermore, the nonlinear dynamics are observed to be tunable by changing the binding energy of the valence-band-maximum, as confirmed by Simpleman model calculations. We believe that such extreme nonlinear photoemission from nanotips offers a new means of producing extreme temporal-spatial resolved electron pulses. These results additionally provide a new design philosophy for attosecond electronics and optics by making use of tunable band structures in nanomaterials.