Orbital loop currents have been theoretically proposed to emerge in a variety of quantum materials where strong electronic correlations give rise to novel states of matter.

Over the last two decades, several experimental probes, and in particular polarized neutron diffraction, reported signatures of an unusual magnetic state appearing at the pseudogap onset temperature T* in high-Tc cuprates. This intra-unit cell magnetism (q=0) is characterized by the breaking of time-reversal and inversion symmetries while preserving lattice translational symmetry, and is naturally interpreted in terms of circulating orbital loop currents associated with anapoles (toroidal moments) [1].

More recent polarized neutron diffraction investigations in underdoped, detwinned YBa₂Cu₃O_6+x samples revealed additional short-range magnetic correlations at finite wavevector (q=1/2 magnetism), consistent with a 2 x 2 superstructure of the CuO₂ unit cell. These observations suggest that, beyond the uniform intra–unit-cell magnetism, the pseudogap phase may host a more complex loop current magnetic texture, extending over several CuO₂ unit cells [2-4].

Interestingly, recent neutron diffraction measurements in the kagome superconductor CsV₃Sb₅ further suggest possible loop current patterns developing within the vanadium triangles [4].

[1] P. Bourges et al, C.R. Phys S22, 1-25 (2021).

[2] D. Bounoua et al, Nat. Comm. Phys 5, 268 (2022); Phys. Rev. B 108, 214408 (2023).

[3] D. Bounoua et al, Int. J. Mod. Phys. B 2640023 (2026).

[4] W. Liège et al Phys. Rev. B 110, 195109 (2024).