Yuki Shiomi
Magnetopiezoelectric effect [1,2], which refers to a linear strain response to electric currents and its inverse response in low-symmetric magnetic metals, is a generalization of magnetoelectric effects in insulators to metals. In metallic materials with high conduction-electron densities, static (dc) piezoelectric responses are not allowed, even if the metals have a symmetry group low enough to support a static polarization. This is because the static surface charge density is screened out by bulk conduction electrons. However, it was recently proposed [1] that dynamic distortion can arise in response to electric currents without screening effects in antiferromagnetic metals that simultaneously break time-reversal and spatial-inversion symmetries. Note that another magnetopiezoelectric effect of a topological origin has also been proposed recently [2].
Here, we have experimentally studied the magnetopiezoelectric effect [3-5] in antiferromagnetic conductors with low crystal symmetries: EuMnBi2 [3,5] (TN = 315 K) and CaMn2Bi2 [4] (TN = 150 K). Using laser Doppler vibrometry at low temperatures, we found that dynamic displacements emerge along the [110] direction upon application of ac electric currents in the c direction in EuMnBi2 below TN [3,5]. The displacement signals showing up in response to the electric current increase in proportion to the applied electric currents. We confirmed that such displacements are not observed along the c direction of EuMnBi2 or EuZnBi2 with nonmagnetic Zn ions, consistent with the symmetry requirement of the magnetopiezoelectric effect [1]. As temperature increases from the lowest temperature, the displacement signals decrease monotonically, showing that magnetopiezoelectric signals are larger for higher conductivity states as opposed to the conventional piezoelectric effect.
[2] D. Varjas, A. G. Grushin, R. Ilan, and J. E. Moore, Phys. Rev. Lett. 117, 257601 (2016).
[3] Y. Shiomi, H. Watanabe, H. Masuda, H. Takahashi, Y. Yanase, and S. Ishiwata, Phys. Rev. Lett. 122, 127207 (2019).
[4] Y. Shiomi, Y. Koike, N. Abe, H. Watanabe, and T. Arima, Phys. Rev. B 100, 054424 (2019).
[5] Y. Shiomi, H. Masuda, H. Takahashi, and S. Ishiwata, Sci. Rep. 10, 7574 (2020).