  In many quantum materials, strong electron correlations lead to the emergence
of new states of matter. In particular, the study in the last decades of the
complex phase diagram of high temperature superconducting cuprates highlighted
intra-unit-cell electronic instabilities breaking discrete Ising-like
symmetries, while preserving the lattice translation invariance. Polarized
neutron diffraction experiments have provided compelling evidences supporting a
new form of intra-unit-cell magnetism, emerging concomitantly with the
so-called pseudogap state of these materials. This observation is currently
interpreted as the magnetic hallmark of an intra-unit-cell loop current order,
breaking both parity and time-reversal symmetries. More generally, this
magneto-electric state is likely to exist in a wider class of quantum materials
beyond superconducting cuprates. For instance, it has already been already
observed in hole-doped Mott insulating iridates or in the spin liquid state of
hole-doped 2-leg ladder cuprates.
