resulting in ultrahigh carrier mobilities, long mean free paths, and anomalous quantum Hall effects. [3][4][5][6][7] The most important advantage of graphene is the tunability of the carrier densities, which can be easily controlled by a gate bias or doping. [8][9][10][11][12] Consequently, graphene has been applied as convenient tunable terahertz (THz) metamaterials. [9,10,13,14] In photonics, the optical properties of graphene have been discussed with the surface plasmon model, corresponding to the Drude model with the free carrier concept. In general, in the plasmon model, the restoring force by the displacement from equilibrium is neglected to simplify the solution of the Maxwell equation. It has successfully been applied to the analysis of optical conductivity in metals including graphene over the THz regime [15][16][17][18] as the frequency of electromagnetic waves is significantly higher, compared to the plasma frequency. Recently, the applications of graphene have been extended to microwave absorption in the gigahertz (GHz) regime. [19,20] However, in most of these studies, the optical conductivity of graphene, related to the optical absorption, is discussed with the Debye model [21] or free carrier model. [22] The effective mass of electrons in graphene is extremely small, resulting in a high plasma frequency, comparable to the GHz regime. Hence, the analysis of the optical conductivity of graphene in the GHz regime should be modified from the free carrier model to the plasma carrier model considering the restoring force.In contrast, the field-induced time-resolved microwave conductivity (FI-TRMC) technique has recently been applied to complex permittivity analysis for organic semiconductors, leading to the assessment of the trap depth for charge carriers. [23] FI-TRMC is a microwave-based alternating current technique to evaluate the dielectric loss of materials with a resonant cavity. [23][24][25][26][27] In contrast to direct current (DC) methods represented by field-effect transistor (FET) and Hall effect measurements, FI-TRMC is advantageous in that it avoids the effect of extrinsic factors because of the small displacement distance of charge carriers. [28] For complex permittivity analysis with FI-TRMC, the real change in permittivity is estimated simultaneously with the dielectric loss, providing a detailed range of charge transport characteristics in the materials. FI-TRMC is suitable for investigation of the electronic properties The relaxation time and mobility of electrons on graphene are deduced quantitatively by complex permittivity analysis with microwave dielectric loss spectroscopy. Hexagonal graphene sheets with uniform domain sizes from 6 to 30 µm, which target the mean free path of electrons on graphene based on the significantly longer turnover time of microwave probing at gigahertz (GHz) frequencies as compared to the relaxation time of electrons, are employed to determine the factors for carrier relaxation at the intradomain and grain boundaries. The changes in the complex permittiv...

Charge carriers injected onto a graphene layer are perturbed by the probing microwave as rippling waves. By tracing these waves the mass and mobility of electrons can be determined experimentally in the technique referred as Field‐Induced Time‐Resolved Microwave Conductivity (FI‐TEMC) measurement, as shown by Shu Seki and co‐workers in article number https://doi.org/10.1002/adom.201701402.