Laser-induced Modulation of Conductance in Graphene with Magnetic Barriers Enables Photon-assisted Electron Transport

The behaviour of electrons in materials is fundamentally shaped by external forces, and researchers are continually seeking new ways to control this behaviour with precision. Rachid El Aitouni, Miloud Mekkaoui, and colleagues, including Pablo Díaz and David Laroze, have demonstrated a novel method for manipulating electron flow through graphene using a combination of magnetic barriers and laser light. Their work reveals that by illuminating the space between two magnetic barriers, graphene’s conductance can be actively modulated, creating a system where electron transport switches between conventional transmission and a state dominated by photon exchange. This hybrid approach, which balances optical pumping with magnetic filtering, not only enables highly tunable resonances and even perfect transmission under specific conditions, but also opens new avenues for designing advanced electronic devices with unprecedented control over electron behaviour.

raphene sheet encounters two magnetic barriers with a region between them continuously driven by laser light. This illuminated section does not act as a static obstacle, but instead functions as a Floquet cavity, opening new transport channels through controlled photon absorption and emission. The research combines theoretical modelling with experimental observation to track electron transmission through both the main energy band and the emerging photon-assisted sidebands. Results show the laser does more than modify the potential; it reshapes how electrons interact between the magnetic barriers, enabling a switch from ordinary transmission to transport dominated by photon exchange.

Tunable Graphene Properties via External Fields

This research details investigations into the electronic and optical properties of graphene and related two-dimensional materials, particularly focusing on how these materials can be manipulated by external fields, such as light and electric fields, to create novel devices. The work explores phenomena like the Franz-Keldysh effect, which allows for tunable optical absorption, and the creation of tunable electronic devices. A significant portion of the research involves theoretical calculations and computational modelling, supported by experimental validation. The ultimate goal is to develop advanced materials and devices for applications in areas like optoelectronics, terahertz technology, and potentially quantum computing.

The research focuses on graphene, but also extends to other two-dimensional materials and heterostructures. A key area of investigation is the Franz-Keldysh effect, enabling tunable optical absorption and the creation of optical modulators. The team explores how this effect can be enhanced and controlled, and investigates the control of light absorption in graphene and related materials, achieved through the application of electric fields, light fields, and the creation of specific material structures. The research also explores the potential of graphene-based devices for generating and detecting terahertz radiation, with applications in imaging, spectroscopy, and communications.

Combining different two-dimensional materials to create heterostructures with tailored properties is also explored. Specific areas of investigation include how electric fields modify the band structure and optical properties of graphene, and the interaction of light with graphene, including absorption, reflection, and transmission. The team also investigates band structure engineering, modifying the electronic band structure of graphene to achieve desired properties. Computational methods, such as Density Functional Theory and the Tight-Binding Model, are used to calculate the electronic structure of materials. This research is pushing the boundaries of graphene-based materials and devices, aiming to create new technologies with enhanced performance and functionality.

Tunable Electron Control via Magnetic and Laser Fields

Scientists have demonstrated a novel method for controlling electron movement in graphene using a combination of magnetic and laser fields, achieving tunable transmission and strong confinement of electrons. The research reveals that by applying magnetic barriers separated by a laser-irradiated region, electrons exhibit unique transport characteristics distinct from systems using only magnetic or laser barriers. Experiments show that the laser field quantizes the energy spectrum, creating two distinct transmission processes: one involving photon exchange and one without, fundamentally altering electron behavior. The team measured that increasing the distance between the magnetic barriers decreases transmission, indicating a reduction in the number of electrons crossing the barrier, consistent with observations in double magnetic and double laser barrier systems.

This reduction in transmission leads to a corresponding decrease in conductance, demonstrating precise control over electron flow. Importantly, the study reveals the emergence of Fano resonances and angle-dependent transmission zeros, features impossible to achieve with single magnetic or laser barriers alone. Data shows that the combined system exhibits a qualitative change in resonance structure and carrier confinement, due to interference between cyclotron momentum filtering from the magnetic barriers and discrete Floquet sideband channels created by the laser region. Researchers observed perfect transmission in a left-shifted region, alongside anti-resonances (perfect reflection) in a small region, demonstrating highly tunable control over electron transport. This work establishes a new approach to electron steering by balancing optical pumping and magnetic momentum filtering, opening possibilities for advanced nanoelectronic devices and quantum circuits.

Tunable Resonances Via Laser-Magnetic Control

This research demonstrates a novel approach to electron transport, achieving control over electron movement through the combined application of magnetic barriers and laser illumination. By integrating these elements, the team uncovered a system where laser light doesn’t simply modify a potential, but actively reshapes electron interactions, enabling a transition from standard transmission to transport dominated by photon exchange. The study reveals that this hybrid configuration supports unique interference effects, producing Fano resonances and angle-dependent transmission characteristics not observed in systems with only magnetic or laser barriers. Specifically, the researchers found that the interplay between magnetic confinement and photon pumping allows for tunable resonances and, under certain conditions, even perfect electron transmission despite strong magnetic fields. Analysis of the system’s conductance revealed a saturation plateau, indicating a limit to current flow, and showed that lower energy electrons are effectively blocked by the magnetic regions. The team focused their analysis on the central energy band and its immediate sidebands, finding that transmission without photon exchange generally prevails, though photon-assisted transmission becomes more probable with increased laser intensity.