The effective mass of Abrikosov vortices in superconductors remains a challenging problem with limited experimental verification. Here, we observe circular dichroism in magnetic field, which we relate to the vortex mass. At 10 T, we demonstrate the emergence of dichroism with decreasing temperature in two YBaCuO thin films of different doping. The experimental results can be explained within a theoretical model of Kopnin-Vinokur [1] that takes into account the vortex mass and predicts it as a tensor. At THz frequencies, both diagonal and off-diagonal masses are complex, which reflects a delay between a change of the vortex velocity and that of the total momentum of quasiparticles in its core. The off-diagonal mass describes a property common in anisotropic systems that the velocity of an excitation is not parallel with its momentum. For YBaCuO at 45 K, in the zero-frequency limit, the diagonal mass of vortices amounts to 2 x 10⁸ electron masses per centimeter (m_e/cm), while the off-diagonal one reaches 5 x 10⁸ m_e/cm [2,3].

[1] N. Kopnin, and V. M. Vinokur, Phys. Rev. Lett. 81, 3952 (1988)

[2] R. Tesař, M. Šindler, C. Kadlec, P. Lipavský, L. Skrbek, and J. Koláček, “Mass of Abrikosov vortex in high‐temperature superconductor YBa₂Cu₃O_7−δ,” Sci. Rep. 11, 21708 (2021)

[3] R. Tesař, M. Šindler, P. Lipavský, J. Koláček, and C. Kadlec, “Perspective on the vortex mass determination in superconductors using circular dichroism”, IEEE Trans. Appl. Supercond. 34, 7200305 (2024)