Dielectric Haloscopes: A New Way to Detect Axion Dark Matter

We propose a new strategy to search for dark matter axions in the mass range of $40–400\mu \mathrm{eV}$ by introducing dielectric haloscopes, which consist of dielectric disks placed in a magnetic field. The changing dielectric media cause discontinuities in the axion-induced electric field, leading to the generation of propagating electromagnetic waves to satisfy the continuity requirements at the interfaces. Large-area disks with adjustable distances boost the microwave signal (10–100 GHz) to an observable level and allow one to scan over a broad axion mass range. A sensitivity to QCD axion models is conceivable with 80 disks of $1{\mathrm{m}}^2$ area contained in a 10 T field.

Figure 1

A dielectric haloscope consisting of a mirror and several dielectric disks placed in an external magnetic field ${\mathbf{B}}_e$ and a receiver in the field-free region. A parabolic mirror (not shown) could be used to concentrate the emitted power into the receiver. Internal reflections are not shown.

Figure 2

Boost factor $\beta ({\nu }_a)$ for configurations optimized for $\mathrm{\Delta }{\nu }_{\beta }=200$, 50, and 1 MHz (red, blue, and gray) centered on 25 GHz using a mirror and 20 dielectric disks ($d=1\mathrm{mm}$, $\epsilon =25$).

Figure 3

Two examples of the discovery potential (light and dark blue) of our dielectric haloscope using 80 disks ($\epsilon =25$, $A=1{\mathrm{m}}^2$, $B_e=10\mathrm{T}$, $\eta =0.8$, $t_R=1\text{day}$) with quantum limited detection in a 3 yr campaign. We also show exclusion limits (gray) and sensitivities (colored) of current and planned cavity haloscopes [16, 17, 32, 33, 34, 35, 36]. (Upper inset) The initial angle ${\theta }_I$ required in scenario A [37]. (Lower inset) The $f_a$ value corresponding to a given $m_a$. The three black lines denote $|C_{a\gamma }|=1.92$, 1.25, 0.746. Note that scenario B predicts $50\mu \mathrm{eV}\lesssim m_a\lesssim 200\mu \mathrm{eV}$ [12, 38].