Light-field driven currents in graphene (1607.04198v1)

Abstract: Ultrafast electron dynamics in solids under strong optical fields has recently found particular attention. In dielectrics and semiconductors, various light-field-driven effects have been explored, such as high-harmonic generation, sub-optical-cycle interband population transfer and nonperturbative increase of transient polarizability. In contrast, much less is known about field-driven electron dynamics in metals because charge carriers screen an external electric field in ordinary metals. Here we show that atomically thin monolayer Graphene offers unique opportunities to study light-field-driven processes in a metal. With a comparably modest field strength of up to 0.3 V/{\AA}, we drive combined interband and intraband electron dynamics, leading to a light-field-waveform controlled residual conduction current after the laser pulse is gone. We identify the underlying pivotal physical mechanism as electron quantum-path interference taking place on the 1-femtosecond ($10^{-15}$ second) timescale. The process can be categorized as Landau-Zener-St\"uckelberg interferometry. These fully coherent electron dynamics in graphene take place on a hitherto unexplored timescale faster than electron-electron scattering (tens of femtoseconds) and electron-phonon scattering (hundreds of femtoseconds). These results broaden the scope of light-field control of electrons in solids to an entirely new and eminently important material class -- metals -- promising wide ramifications for band structure tomography and light-field-driven electronics.

• The paper demonstrates that ultrafast, CEP-dependent electron currents in graphene can be generated using few-cycle laser pulses via quantum path interference.
• It employs a robust nearest-neighbor tight-binding model alongside numerical simulations that accurately reproduce nonlinear current responses with varying field strength.
• The findings pave the way for integrated optoelectronic devices and offer new insights into ultrafast light-matter interactions in two-dimensional materials.

Overview of Light-Field Driven Currents in Graphene

The paper "Light-field driven currents in graphene" presents a detailed investigation into the dynamics of electron currents induced by ultrafast laser pulses in monolayer graphene. Through meticulous experimentation, the authors demonstrate the potential to manipulate electron currents in graphene using few-cycle laser pulses, emphasizing graphene's unique properties as a conductive medium with negligible screening effects at optical frequencies.

Graphene's distinct electronic properties, such as high carrier mobility and a low carrier concentration relative to conventional metals, make it an exemplary platform for studying light-field-driven electron dynamics. This paper elucidates how graphene, under sub-optical-cycle laser excitations, allows for coherent electron wave packet evolution through combined interband and intraband processes. Particularly, these processes in graphene occur on a timescale faster than electron scattering events, such as electron-electron and electron-phonon interactions, underscoring the material's potential for ultrafast electronics applications.

Key Findings

The authors leverage graphene's Dirac-cone dispersion relation, conducting experiments using few-cycle, carrier-envelope-phase (CEP) stabilized laser pulses on micro-fabricated graphene stripes. The results show that the induced currents are strongly dependent on the CEP of the laser pulses. Notably, the pivotal mechanism underpinning this current generation is identified as the Landau-Zener-Stückelberg interferometry, where light-induced quantum path interference plays a crucial role.

The findings are well-supported by a robust theoretical framework based on a nearest-neighbor tight-binding model, further corroborated by numerical simulations. These simulations reproduce essential experimental features: a nonlinear increase in CEP-dependent current with field strength and the intriguing change in current direction with increasing peak electric field strength for linearly polarized light. Notably, numerical results align closely with experimental data, confirming the model's validity for investigating light-matter interactions in graphene.

Implications and Future Directions

The exploration of light-field-driven currents in graphene holds potential implications for developing advanced electronic devices, particularly in semimetallic 2D materials. The ability to control electron dynamics at such a high-speed level provides a promising approach for band structure characterizations and the design of innovative optoelectronics. This work substantiates the feasibility of integrating optical and electronic functionalities on a single platform using graphene.

For theoretical advancement, this paper opens pathways to examine correlated electron behavior on intrinsic timescales, offering fresh perspectives for exploring fundamental electron dynamics in solids. Further research could focus on extending this approach to paper other 2D materials, expanding our understanding of ultrafast processes and their practical applications. Exploring the impact of additional factors, such as multi-band interactions and electron correlation effects, may yield further insights into the complexities of light-induced electron dynamics.

In conclusion, this paper offers a comprehensive analysis of the principles governing light-field-driven currents in graphene, paving the way for future innovations in ultrafast electronics and optics. The insights gleaned from this research could aid in harnessing the unique properties of graphene and similar materials, propelling advancements in the development of next-generation electronic devices.