Broadband terahertz conductivity and polarization dynamics of single-crystal diamond

We present broadband terahertz studies of high-purity single-crystal diamond grown by chemical vapor deposition over a frequency range of 0.2–4.5 THz. The experimentally characterized conductivity exhibits a pronounced non-monotonic frequency dependence that cannot be described by the conventional Drude model. To capture this behavior, we employ a constrained Drude–Lorentz (CDL) model, which incorporates free-carrier transport and an effective off-resonant polarization contribution beyond the measured spectral window. The real part of the dielectric function yields ε1 ≈ 5.64, consistent with the known static dielectric constant of diamond. The CDL model accurately reproduces the broadband response, from which a carrier mobility of ∼2963 cm2/V s and a carrier density of ∼1.05 × 1013 cm−3 are obtained. These results show that the broadband nature of terahertz time-domain spectroscopy is essential for resolving coupled carrier–polarization dynamics in high-purity diamond.