Emerging axion detection in artificial magnetoelectric materials

TL;DR

This work introduces a novel axion-detection strategy that leverages symmetry-broken magnetoelectric materials with a linear coupling between polarization and magnetization to amplify weak axion-induced signals without requiring strong external magnetic fields. The authors develop a theoretical framework linking the axion field to magnetoelectric order, and implement two experimental modalities—SQUID-based magnetization measurements and direct magnetoelectric coupling measurements in Sr2IrO4 strain-gradient thin films—to constrain axion-electron and axion-photon couplings. By combining magnetization data and direct ME measurements, they derive exclusion limits on $g_{a\gamma\gamma}$ and $g_{ae}$ and demonstrate the viability of a field-free, tunable platform for axion searches in condensed-matter systems. The study highlights future opportunities in material design, multilayer architectures, and resonance-enhanced detection pathways to expand sensitivity to a broad axion mass range and deepen our understanding of dark matter through magnetoelectric effects.

Abstract

Axions are considered a key component of dark matter, characterized by very weak couplings to fermions and Chern-Simons couplings to gauge fields. We propose a novel detection mechanism based on symmetry-breaking magnetoelectric materials with a linear axionic coupling between magnetization and ferroelectric polarization. The focus is on a strain gradient Sr2IrO4 film, where the breaking of space-inversion symmetry results in an emergent polar phase and an out-of-plane magnetic moment, exhibiting a flexomagnetoelectric effect. In this material, the linear P||M enables a direct coupling between the external axion field and the intrinsic axion-like field, which amplifies the weak electromagnetic signals induced by axions, paving the way for pioneering axion detection. In contrast to conventional detection techniques, this mechanism is expected to enhance the sensitivity of the axion-electron and axion-photon coupling, providing a novel platform for axion detection and advancing the study of dark matter through the magnetoelectric effect.

Figures (5)

• Figure 1: (a) The magnetoelectric material exhibits parallel polarization (P) and magnetization (M), corresponding to the breaking of spatial inversion symmetry and time-reversal symmetry. (b) Enlarged view within the circle of (a), where the external axion field effectively couples with the internal axion-like field in the material. (c) Under axion dark matter excitation, the external axion field couples with the intrinsic P·M mode of the magnetoelectric material, modulating its magnetoelectric response.
• Figure 2: (a) Schematic of the SQUID measurement system, when the sample moves within the superconducting detection coil, the magnetic flux through the coil changes, inducing an electromotive force that reflects the sample’s magnetic moment. The magnetic flux is directly coupled to the SQUID sensor, where the Josephson junctions convert the flux variation into a measurable voltage signal. (b) Time-dependent magnetization curve at 20 K.
• Figure 3: (a) Schematic of the magnetoelectric coupling measurement system. Electrodes are fabricated on the top and bottom surfaces of the $\text{Sr}_2\text{IrO}_4$ sample to collect electrical signals. The orange rings denote Helmholtz coils, which are driven by an AC power supply to generate an axial alternating magnetic field. Under this field, an alternating electrical signal is induced between the top and bottom electrodes of the sample and detected using a lock-in amplifier. (b) Time-dependent magnetoelectric response curve at 20 K.
• Figure 4: Constraints on the coupling factor $g_{a\gamma\gamma }$. The red and pink exclusions are obtained in our experiments, which utilize an external magnetic field of approximately 1000 Oe. The size of the test sample is $300~\text{nm}\times2.5~\text{mm}\times2.5~\text{mm}$. The SQUID measurement system (ME Materials) obtains the red exclusion, and the magnetoelectric coupling measurement system (MECMS) obtains the pink exclusion. For the red exclusion, the integration time of $M$ is 10 seconds, while for the pink exclusion, the integration time of $\theta$ is 1 second. The projection of Magnetoelectric Materials is based on an SNR=3 criterion. The size of the magnetoelectric material sample for the projection is $0.1\times0.1\times0.01~\text{m}^3$. The integration time of the projection is one year. We consider the 95$\%$ C.L. exclusion limit. The bound of the Globular cluster comes from Reference Ayala:2014pea. The bounds of CAST come from Reference CAST:2024eil. The projection of WISPLC is based on Reference Zhang:2021bpa. The projection of IAXO comes from Reference IAXO:2019mpb. The yellow lines represent Kim-Shifman-Vainshtein-Zakharov (KSVZ) and Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axion models, and the yellow region represents the hadronic band.
• Figure 5: Constraints on the coupling factor $g_{ae }$. The red and pink exclusion is obtained in our experiments, which utilize an external magnetic field of approximately 1000 Oe. The SQUID measurement system obtains the red exclusion, and the magnetoelectric coupling measurement system (MECMS) obtains the pink exclusion. The size of the test sample is $300~\text{nm}\times2.5~\text{mm}\times2.5~\text{mm}$. For the red exclusion, the integration time of $M$ is 10 seconds, while for the pink exclusion, the integration time of $\theta$ is 1 second. The projection of Magnetoelectric Materials is made assuming SNR=3. The size of the magnetoelectric material sample for the projection is $0.1\times0.1\times0.01~\text{m}^3$. The integration time of the projection is one year. We consider the 95$\%$ C.L. exclusion limit. The bounds of XENONnT (Solar axions) and XENONnT (ALP DM) come from Reference XENON:2022ltv. The Red giant branch bound is taken from Reference Capozzi:2020cbu. The constraint of Solar neutrinos comes from Reference Gondolo:2008dd.