Electronic properties of neutron-irradiated hexagonal boron nitride measured by terahertz magneto-optical experiment

Hexagonal boron nitride (hBN) has been proposed as an ideal material for solid-state neutron detector because of its exceptional and phenomenal physical properties such as having a large neutron scattering cross-section. Here we employ the terahertz time-domain spectroscopy to study the magneto-optical (MO) properties of neutron-irradiated pyrolytic boron nitride in magnetic field regime from 0 to 8T at a fixed temperature of 80 K. Applying the optical polarization tests in the Faraday geometry, we measure the real and imaginary parts of the left- and right-handed circularly polarized dynamic dielectric function ${∊}_{\pm }\left(\omega \right)$ and MO conductivities ${\sigma }_{\pm }\left(\omega \right)$ for hBN samples irradiated by neutrons with different fluences. By fitting our experimental results with the theoretical formulas for ${∊}_{\pm }\left(\omega \right)$ and ${\sigma }_{\pm }\left(\omega \right)$ of an electronic gas, we can determine magneto-optically the basic electronic parameters of neutron-irradiated hBN such as the static dielectric constant ${\epsilon }_b$, the carrier density n, the carrier relaxation time $\tau$, the photon-induced electronic localization factor $\alpha$, and the effective carrier mass $m^{\ast }$. The effects of neutron irradiation and the magnetic field B on these parameters are examined and analyzed. We find that the MO conductivities for neutron-irradiated hBN can be reproduced by the MO Drude-Smith formula. We show that the presence of a B-field can result in larger ${\epsilon }_b$ and $\tau$, smaller n and $\alpha$, and heavier $m^{\ast }$. The outcomes of this study can provide valuable insights into the basic electronic and optoelectronic properties of neutron-irradiated hBN.