Could a laser field lead to the much sought-after tunable band gaps in graphene? By using Floquet theory combined with Green's functions techniques, we predict that a laser field in the mid-infrared range can produce observable band gaps in the electronic structure of graphene. Furthermore, we show how they can be tuned by using the laser polarization. Our results could serve as a guidance to design optoelectronic nanodevices.

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Tuning laser-induced band gaps in graphene

Beginning with an introduction to carbon-based nanomaterials, their electronic properties, and general concepts in quantum transport, this detailed primer describes the most effective theoretical and computational methods and tools for simulating the electronic structure and transport properties of graphene-based systems. Transport concepts are clearly presented through simple models, enabling comparison with analytical treatments, and multiscale quantum transport methodologies are introduced and developed in a straightforward way, demonstrating a range of methods for tackling the modelling of defects and impurities in more complex graphene-based materials. The authors also discuss the practical applications of this revolutionary nanomaterial, contemporary challenges in theory and simulation, and long-term perspectives. Containing numerous problems for solution, real-life examples of current research, and accompanied online by further exercises, solutions and computational codes, this is the perfect introductory resource for graduate students and researchers in nanoscience and nanotechnology, condensed matter physics, materials science and nanoelectronics.

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Introduction to Graphene-Based Nanomaterials: From Electronic Structure to Quantum Transport

Landauer - Buttiker Formalism Current Noise Non-Stationary Scattering Theory DC Current Generation AC Current Generation Noise of a Dynamical Scatterer Energetics of a Dynamical Scatterer Dynamical Mesoscopic Capacitor Quantum Circuits with Mesoscopic Capacitor as a Particle Emitter

Scattering Matrix Approach to Non-Stationary Quantum Transport

We report on a theoretical study of the effects of time-dependent fields on electronic transport through graphene nanoribbon devices. The Fabry-Perot interference pattern is modified by an ac gating in a way that depends strongly on the shape of the graphene edges. While for armchair edges the patterns are found to be regular and can be controlled very efficiently by tuning the ac field, samples with zigzag edges exhibit a much more complex interference pattern due to their peculiar electronic structure. These studies highlight the main role played by geometric details of graphene nanoribbons within the coherent transport regime. We also extend our analysis to noise power response identifying under which conditions it is possible to minimize the current fluctuations as well as exploring scaling properties of noise with the length and width of the systems.

/pdf/ac-transport-in-graphene-based-fabry-perot-devices-mrkwyukztu.pdf

ac transport in graphene-based Fabry-Pérot devices

We studied the generation of valley dependent current by adiabatic quantum pumping in monolayer graphene in the presence of electric potential barriers, ferromagnetic field and strain. The pumped currents in the two valleys have same magnitudes and opposite directions; thus, a pure valley current is generated. The oscillation of the pumped pure valley current is determined by the Fabry-Perot resonances formed in the structure. In our calculation, the pumped pure valley current can be as high as 50 nA, which is measurable using present technologies. The proposed device is useful for the development of graphene valleytronic devices.

Quantum pumping of valley current in strain engineered graphene

We study the adiabatic quantum pumping characteristics in graphene modulated by two oscillating gate potentials out of phase. The angular and energy dependence of the pumped current (PC) is presented. The direction of the PC can be reversed when a high potential barrier demonstrates stronger transparency than a low one, which results from the Klein paradox. The underlying physics of the pumping process is illuminated.

Quantum pumping with adiabatically modulated barriers in graphene

Cascaded Brillouin lasers based on guided-wave structures are applied across a range of important fields such as optical communications, microwave photonics, and sensing. However, restricted by the volume and available transmission range of the gain medium, the power output and wavelength diversity of guided-wave Brillouin devices are somewhat limited. In this work, we report the design and development of a cascaded Brillouin laser based utilizing a free-space optical layout with a diamond crystal as the Brillouin gain medium. A quasi-continuous-wave, 1  μm laser was used as the pump laser, and Raman wavelength conversion is used as an intermediate process to facilitate stimulated Brillouin scattering with a low threshold. When the output transmission of the diamond cavity is 0.37% and the incident pump power is 220 W, cascading of the Brillouin–Stokes field to the eighth Stokes and the seventh anti-Stokes orders was observed. By adjusting the cavity length, the order of the cascaded Brillouin laser output is controlled. A comprehensive analysis of the Brillouin generation process and the cascade of Stokes orders is undertaken for different incident pump powers and cavity lengths. This work is expected to enable practical applications of high-power Brillouin lasers and Brillouin frequency combs.

Enhanced stimulated Brillouin scattering utilizing Raman conversion in diamond

We study the adiabatic quantum pumping characteristics in the graphene modulated by two oscillating gate potentials out of phase. The angular and energy dependence of the pumped current is presented. The direction of the pumped current can be reversed when a high barrier demonstrates stronger transparency than a low one, which results from the Klein paradox. The underlying physics of the pumping process is illuminated.

Huiming Chen

Papers

Quantum pumping with adiabatically modulated barriers in graphene

Enhanced stimulated Brillouin scattering utilizing Raman conversion in diamond

Quantum pumping with adiabatically modulated barriers in graphene