Speaker
Description
Optical probes are naturally well suited to detecting broken symmetries, including time-reversal symmetry (T), and are frequently used in this way, for example, to map ferromagnetic domains. But the conditions under which optics can detect T - breaking in antiferromagnets with no net magnetization are far more subtle. The key distinction is whether the effect of T can be undone by a simple translation (S_(1/2)); if it can, the product 〖TS〗(1/2) is a symmetry of the system and T-breaking is usually invisible to bulk probes. In contrast, antiferromagnets that do not preserve 〖TS〗(1/2) display a range of bulk T- breaking phenomena, such as the magnetoelectric and piezomagnetic effect.
But what exactly does “bulk” mean? And more specifically, are optical probes “bulk”: can they detect T- breaking in 〖TS〗(1/2) - invariant antiferromagnets? We address these questions by comparing three antiferromagnets: non-collinear EuIn2As2 and altermagnetic MnTe that break 〖TS〗(1/2) and MnBi2Te4 that does not. In EuIn2As2 we show how an unconventional optical probe, linear magneto-birefringence, can reveal symmetry breaking invisible to more standard measurements [1-3]. In MnTe, simultaneous measurements of linear and circular dichroism reveal microscopic orientation of the T - breaking order parameter [4]. In MnBi2Te4, we demonstrate how perhaps the most standard optical probe of magnetism, reflection circular dichroism, can in fact detect antiferromagnetism even when 〖TS〗_(1/2) is preserved in the bulk [5].
Together, these experiments demonstrate both the power and the versatility of optics as a probe of symmetry breaking in quantum materials.
References
[1] Sunko, V.; Sun, Y.; Vranas, M.; Homes, C. C.; Lee, C.; Donoway, E.; Wang, Z.-C.; Balguri, S.; Mahendru, M. B.; Ruiz, A.; Gunn, B.; Basak, R.; Blanco-Canosa, S.; Schierle, E.; Weschke, E.; Tafti, F.; Frano, A.; Orenstein, J., Phys. Rev. B, 107, 144404 (2023).
[2] Donoway, E.; Trevisan, T. V.; Liebman-Peláez, A.; Day, R. P.; Yamakawa, K.; Sun, Y.; Soh, J. R.; Prabhakaran, D.; Boothroyd, A. T.; Fernandes, R. M.; Analytis, J. G.; Moore, J. E.; Orenstein, J.; Sunko, V., Phys. Rev. X, 14, 031013 (2024)
[3] Sunko, V.; Orenstein, J., arXiv, 2511.16421 (2025)
[4] Liebman-Peláez, A.; Kruppe, J.; Regmi, R. B.; Ghimire, N. J.; Sun, Y.; Mazin, I. I.; Noad, H. M. L.; Analytis, J.; Sunko, V.; Orenstein, J., arXiv, 2604.07653, (2026)
[5] Sunko, V.; Ahsanullah, S.; Jain, V.; Weber, S.; Kumaran, S.; Yan, J.-Q.; Orenstein, J.; Ovchinnikov, D., arXiv, 2504.16167 (2025)