Dielectric properties of single-crystal calcium tungstate

Le résumé fourni par la source

This investigation employed microwave whispering gallery mode (WGM) analysis to characterize the dielectric properties of a cylindrical, single-crystal sample of calcium tungstate (CaWO$_4$). Through investigation of quasi-transverse\hyp{}magnetic and quasi-transverse\hyp{}electric mode families, we can assess loss mechanisms and relative permittivity from room temperature down to cryogenic conditions. We report the biaxial permittivity values of $ε_{||} = 9.029 \pm 0.009$ and $ε_{\perp} = 10.761 \pm 0.01$ at $295$ K, and $ε_{||} = 8.794 \pm 0.009$ and $ε_{\perp} = 10.440 \pm 0.01$ at $4$ K. Components are denoted with respect to the c\hyp{}axis of the crystal unit cell. The parallel component agrees well with the published literature at MHz frequencies; however, the perpendicular component is $4.8$\% lower. The WGM technique offers greater precision, with accuracy limited primarily by the uncertainty in the crystal's dimensions. WGMs also serve as sensitive probes of lattice dynamics, enabling monitoring of temperature-dependent loss mechanisms. At room temperature, the measured loss tangents were $\tanδ_{||}^{295,\mathrm{K}} = (4.1 \pm 1.4) \times 10^{-5}$ and $\tanδ_{\perp}^{295,\mathrm{K}} = (3.64 \pm 0.92) \times 10^{-5}$. Upon cooling to 4 K, the loss tangents improved by approximately two orders of magnitude, reaching $\tanδ_{||}^{4,\mathrm{K}} = (1.56 \pm 0.52) \times 10^{-7}$ and $\tanδ_{\perp}^{4,\mathrm{K}} = (2.05 \pm 0.79) \times 10^{-7}$. These cryogenic values are higher than those reported in prior studies, likely due to a magnetic loss channel associated with an unidentified paramagnetic spin ensemble. These findings have implications for the use of CaWO$_4$ in applications such as spin-based quantum systems and cryogenic bolometry, highlighting the potential of WGMs for novel sensing applications.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.