Dielectric Properties of Single Crystal Calcium Tungstate

• URL: http://arxiv.org/abs/2507.21662v1
• Date: Tue, 29 Jul 2025 10:17:54 GMT
• Title: Dielectric Properties of Single Crystal Calcium Tungstate
• Authors: Elrina Hartman, Michael E Tobar, Ben T McAllister, Jeremy F Bourhill, Andreas Erb, Maxim Goryachev,
• Abstract summary: Investigation employed microwave whispering gallery mode (WGM) analysis to characterize the dielectric properties of a cylindrical, single-crystal sample of calcium tungstate (CaWO$_4$)<n>WGM technique offers greater precision, with accuracy limited primarily by the uncertainty in the crystal's dimensions.<n>Findings have implications for the use of CaWO$_4$ in applications such as spin-based quantum systems and cryogenic bolometry.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: 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 $\epsilon_{||} = 9.029 \pm 0.09$ and $\epsilon_{\perp} = 10.761 \pm 0.11$ at $295$ K, and $\epsilon_{||} = 8.797 \pm 0.088$ and $\epsilon_{\perp} = 10.442 \pm 0.104$ 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 $\tan\delta_{||}^{295,\mathrm{K}} = (4.1 \pm 1.4) \times 10^{-5}$ and $\tan\delta_{\perp}^{295,\mathrm{K}} = (3.64 \pm 0.92) \times 10^{-5}$. Upon cooling to 4 K, the loss tangents improved by approximately two orders of magnitude, reaching $\tan\delta_{||}^{4,\mathrm{K}} = (1.56 \pm 0.52) \times 10^{-7}$ and $\tan\delta_{\perp}^{4,\mathrm{K}} = (2.05 \pm 0.79) \times 10^{-7}$. 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.

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