This study investigates the charge dynamics in graphene using infrared (IR) spectroscopy, focusing on gated devices. The researchers observed significant departures from the expected behavior of Dirac fermions in idealized, free-standing graphene, indicating the importance of many-body interactions. Key findings include: 1. **Reflectance and Transmission Spectra**: The reflectance and transmission spectra of graphene samples were measured as a function of gate voltage at 45K. At the charge neutrality point, the monolayer graphene significantly modified the interference minimum of the substrate, suppressing the substrate's reflectance by up to 15%. 2. **Conductivity Analysis**: The optical conductivity of charge-neutral graphene was extracted from multilayer analysis, showing agreement with the theoretical prediction of a constant "universal" 2D conductivity. However, below 2E_F (the energy at which interband transitions occur), significant residual conductivity was observed, which could be attributed to many-body interactions. 3. **Fermi Energy and Velocity**: The Fermi energy (2E_F) was extracted from the conductivity spectra, revealing a √V dependence, consistent with the behavior of Dirac quasiparticles. The Fermi velocity (v_F) was also measured, showing a renormalization with voltage, indicating the presence of many-body interactions. 4. **Experimental Deviations**: The study found that the experimental electromagnetic response deviated from a simple single-particle picture, challenging current theoretical conceptions of graphene's fundamental properties and implications for its optoelectronic applications. The research highlights the complex behavior of graphene under applied voltages and the need for further theoretical and experimental investigations to fully understand its electronic properties.This study investigates the charge dynamics in graphene using infrared (IR) spectroscopy, focusing on gated devices. The researchers observed significant departures from the expected behavior of Dirac fermions in idealized, free-standing graphene, indicating the importance of many-body interactions. Key findings include: 1. **Reflectance and Transmission Spectra**: The reflectance and transmission spectra of graphene samples were measured as a function of gate voltage at 45K. At the charge neutrality point, the monolayer graphene significantly modified the interference minimum of the substrate, suppressing the substrate's reflectance by up to 15%. 2. **Conductivity Analysis**: The optical conductivity of charge-neutral graphene was extracted from multilayer analysis, showing agreement with the theoretical prediction of a constant "universal" 2D conductivity. However, below 2E_F (the energy at which interband transitions occur), significant residual conductivity was observed, which could be attributed to many-body interactions. 3. **Fermi Energy and Velocity**: The Fermi energy (2E_F) was extracted from the conductivity spectra, revealing a √V dependence, consistent with the behavior of Dirac quasiparticles. The Fermi velocity (v_F) was also measured, showing a renormalization with voltage, indicating the presence of many-body interactions. 4. **Experimental Deviations**: The study found that the experimental electromagnetic response deviated from a simple single-particle picture, challenging current theoretical conceptions of graphene's fundamental properties and implications for its optoelectronic applications. The research highlights the complex behavior of graphene under applied voltages and the need for further theoretical and experimental investigations to fully understand its electronic properties.