Giant Faraday rotation in single- and multilayer graphene (1007.5286v1)

Abstract: Optical Faraday rotation is one of the most direct and practically important manifestations of magnetically broken time-reversal symmetry. The rotation angle is proportional to the distance traveled by the light, and up to now sizeable effects were observed only in macroscopically thick samples and in two-dimensional electron gases with effective thicknesses of several nanometers. Here we demonstrate that a single atomic layer of carbon - graphene - turns the polarization by several degrees in modest magnetic fields. The rotation is found to be strongly enhanced by resonances originating from the cyclotron effect in the classical regime and the inter-Landau-level transitions in the quantum regime. Combined with the possibility of ambipolar doping, this opens pathways to use graphene in fast tunable ultrathin infrared magneto-optical devices.

• The paper demonstrates that graphene exhibits giant Faraday rotation exceeding 0.1 rad, driven by both classical cyclotron effects and quantum inter-Landau-level transitions.
• Experimental measurements reveal that single-layer graphene shows p-doping with carrier mobility between 2,400 and 3,000 cm²/(V·s), while multilayers display distinct doping profiles.
• The observed magneto-optical behavior, validated by theoretical Drude conductivity models, underlines graphene’s potential for ultrathin, tunable infrared magneto-optical applications.

Giant Faraday Rotation in Single- and Multilayer Graphene

The paper investigates the optical Faraday rotation in graphene, emphasizing its potential as a component in fast tunable ultrathin infrared magneto-optical devices. The paper reveals that a single layer of graphene can exhibit significant magneto-optical effects comparable to those observed in much thicker materials, despite graphene’s atomic scale thickness. The Faraday rotation measured in this paper suggests that the resonances due to cyclotron and inter-Landau-level (LL) transitions play a fundamental role in enhancing the optical response in graphene.

Key Findings

1. Experimental Setup and Measurements: The Faraday rotation was measured using single- and multilayer graphene at relatively low magnetic fields. The rotation angle exceeded 0.1 radians for single-layer graphene, which is a significant effect for a material only one atom thick. This result is attributed to the cyclotron effect in the classical regime and inter-LL transitions in the quantum regime.
2. Doping and Mobility: The paper provided insights into the doping levels and carrier mobility in graphene. For single-layer graphene, p-doping was confirmed through both infrared absorption characteristics and ARPES measurements. The carrier mobility was found to vary between 2,400 and 3,000 cm²/(V·s).
3. Inter-Landau Level Transitions: In multilayer graphene, inter-LL transitions were observed, marked by resonance structures in both Faraday rotation and absorption spectra. These transitions provided evidence of different doping levels across layers, with the innermost layer showing signs of electron doping.
4. Conductivity and Transmission: Using classical Drude formulas, the paper compared the measured Faraday angle and absorption spectra with theoretically predicted values. The conductivity of graphene was measured as a function of photon energy, revealing significant absorption peaks corresponding to quantum Hall effects.

Implications and Future Research

The findings outline the immense potential of graphene in developing advanced magneto-optical technologies. The capacity to achieve notable Faraday rotation from an atomically thin layer underscores the possibility of creating miniaturized optical devices that can operate over a wide range of frequencies. Important to this development is graphene’s capacity for ambipolar doping, which can be fine-tuned. Furthermore, the alignment of experimental observations with theoretical predictions enriches the understanding of graphene’s optical properties and contributes to advancing quantum physics.

Considerations for AI Developments

From an AI perspective, advances in material science as highlighted by this paper could inform new computational models and simulations for material design. AI algorithms could enhance simulations, incorporating complex physical phenomena such as those presented in the paper. This could lead to the rapid identification and design of materials with tailored properties, accelerating the innovation cycle for optoelectronic devices. Future work might leverage AI techniques for a deeper exploration into the electronic interactions within graphene and their implications for circuit elements in quantum computing applications.

In conclusion, this paper adds a significant contribution to our understanding of graphene’s optoelectronic properties, setting a path forward for material science in semiconductor and photonic applications. The demonstrated exceptional magneto-optical properties of graphene, even at a single atomic layer, provide a robust baseline for further innovations in energy-efficient, high-speed optical devices.