Epsilon-near-zero characteristics of near-field radiative heat transfer between α-MoO₃ slabs

Epsilon-near-zero (ENZ) materials, which manifest a wealth of exotic optical characteristics, have attracted significant research interest in recent years. However, these characteristics have rarely been considered in the study of near-field radiative heat transfer (NFRHT). In this work, we investigated the ENZ characteristics of the NFRHT between two symmetric biaxial α-MoO₃ slabs. The numerical results show that the NFRHT is greatly enhanced around the ENZ frequency of 1.604 × 10¹⁴ rad s^-1. Notably, near the other two ENZ frequencies (1.832 × 10¹⁴ rad s^-1 and 1.891 × 10¹⁴ rad s^-1), only the NFRHT between α-MoO₃ slabs of certain thicknesses is enhanced. The reasons can be explained by the fact that the VHPs can be excited in almost all azimuthal angles at angular frequencies of 1.604 × 10¹⁴ rad s^-1 and 1.891 × 10¹⁴ rad s^-1. For the ENZ frequency of 1.832 × 10¹⁴ rad s^-1, the VHPs can be excited at the top and bottom, while the SHPs excited at the left and right sides. It is worth noting that both the hyperbolic and ENZ characteristics affect the NFRHT between α-MoO₃ slabs. Moreover, the excitation is strongly dependent on the thickness of the slab. Our findings contribute to understanding the physical mechanisms underlying the characteristics of the NFRHT at ENZ frequencies.