Proposal to Detect Dark Matter using Axionic Topological Antiferromagnets

Antiferromagnetically doped topological insulators (ATI) are among the candidates to host dynamical axion fields and axion polaritons, weakly interacting quasiparticles that are analogous to the dark axion, a long sought after candidate dark matter particle. Here we demonstrate that using the axion quasiparticle antiferromagnetic resonance in ATIs in conjunction with low-noise methods of detecting THz photons presents a viable route to detect axion dark matter with a mass of 0.7 to 3.5 meV, a range currently inaccessible to other dark matter detection experiments and proposals. The benefits of this method at high frequency are the tunability of the resonance with applied magnetic field, and the use of ATI samples with volumes much larger than $1{\mathrm{mm}}^3$.

Figure 1

(a) The chiral anomaly [42, 43]. $\theta$ is a pseudoscalar chirally coupled to charged Dirac fermions, $\psi$. With applied $B_0$, $\theta$ mixes with $E$ leading to the existence of axion polaritons, ${\varphi }_{\pm }$, in the case of ${\theta }_Q$ and the production of photons in the case of ${\theta }_D$. (b) Resonant enhancement of DA-photon conversion. Colored text refers to Fig. 3. Inside the ATI, the DA couples to the mixed states ${\varphi }_{\pm }$ shown in the shaded circle. Conversion is resonantly enhanced when $p^2={\omega }_a^2={\omega }_{+}(k,B_0{)}^2$, represented by the polariton propagator. At the ATI dielectric boundary, polaritons convert to propagating photons, due to boundary conditions (BCs) [44] represented here by the vertex. (c) The axion-polariton dispersion relation for ${\omega }_{\pm }(k,B_0)$ [45]. Scanning the applied $B_0$ field tunes ${\omega }_{+}(k=0)$ in the range 0.7 to 3.5 meV and scans the resonance.

Figure 2

Axion spin wave Dirac quasiparticle antiferromagnets. (a) Band structure of tuneable Dirac quasiparticles. TI: $\lambda =0.5$, $\delta t_1=0.4$, $Um=0$. AQ: $\lambda =0.5$, $\delta t_1=0.4$, $0<Um<0.25$. Inset: Antiferromagnetic diamond lattice with marked $\mathcal{PT}$ symmetry. (b) Crystal of AF-doped $({\mathrm{Bi}}_{1-x}{\mathrm{Fe}}_x{)}_2{\mathrm{Se}}_3$ exhibits the same magnetic point group symmetry as (a).

Figure 3

Schematics of experimental concept. EM waves are emitted from all material surfaces perpendicular to $B_0$. A mirror and silicon lens focus THz photons from ATI samples onto a single-photon detector located at the center of a log periodic antenna.

Figure 4

Axion parameter space. Vertical lines show the projected sensitivity of our proposal using Fe-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ at $\sim 5\mathrm{T}$ applied field for $10^2\mathrm{s}$ integration time with dark count rate ${\mathrm{\Gamma }}_d=0.001\mathrm{Hz}$. Staged designs are described in the text. Gray shaded regions assume scanning $1\mathrm{T}\le B_0\le 10\mathrm{T}$. The KSVZ and DFSZ axion models are shown as the red band. Existing exclusions from ADMX [17, 18], CAST [27], and supernova 1987A [23] are shown as colored regions.