Coslovich G, Smith R P, Shi S-F, Buss J H, Robinson J T, Wang F, Kaindl R A
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
Sci Rep. 2025 Apr 22;15(1):13935. doi: 10.1038/s41598-025-96448-y.
We employ ultrabroadband terahertz (THz) spectroscopy to expose the high-frequency transport properties of Dirac fermions in monolayer graphene. By controlling the carrier concentration via tunable electrical gating, both equilibrium and transient optical conductivities are obtained for a range of Fermi levels. The frequency-dependent equilibrium response is determined through a combination of time-domain THz and Fourier-transform infrared spectroscopy for energies up to the near-infrared, which also provides a measure of the gate-voltage dependent Fermi level. Transient changes in the real and imaginary parts of the graphene conductivity are electro-optically resolved for frequencies up to 15 THz after near-infrared femtosecond excitation, both at the charge-neutral point and for higher electrostatic-doping levels. Modeling of the THz response provides insight into changes of the carrier spectral weights and scattering rates, and reveals an additional broad-frequency (≈ 8 THz) component to the photo-induced response, which we attribute to the zero-momentum mode of quantum-critical transport observed here in large-area CVD graphene.
我们采用超宽带太赫兹（THz）光谱来揭示单层石墨烯中狄拉克费米子的高频输运特性。通过可调谐电闸控来控制载流子浓度，针对一系列费米能级获得了平衡态和瞬态光电导率。对于高达近红外的能量，通过时域太赫兹光谱和傅里叶变换红外光谱相结合来确定频率相关的平衡响应，这也提供了对栅极电压依赖的费米能级的一种度量。在近红外飞秒激发后，对于电荷中性点以及更高的静电掺杂水平，在高达15太赫兹的频率下，通过电光方法分辨出石墨烯电导率实部和虚部的瞬态变化。对太赫兹响应的建模有助于深入了解载流子光谱权重和散射率的变化，并揭示出光致响应中一个额外的宽频（≈8太赫兹）分量，我们将其归因于在大面积化学气相沉积（CVD）石墨烯中观测到的量子临界输运的零动量模式。
