a − b Anisotropy of the intra-unit-cell magnetic order in YBa$_2$ Cu$_3$O$_{6.6}$
Résumé
Within the complex phase diagram of the hole-doped cuprates, seizing the nature of the mysterious pseudo-gap phase is essential to unravel the microscopic origin of high-temperature superconductivity. Below the pseudo-gap temperature T⋆ , evidences for intra-unit-cell orders breaking the 4-fold rotation symmetry have been provided by neutron diffraction and scanning tunneling spectroscopy. Using polarized neutron diffraction on a detwinned YBa$_2$ Cu$_3$O$_{6.6}$ sample, we here report a distinct a-b anisotropy of the intra-unit-cell magnetic structure factor below T⋆ , highlighting that intraunit-cell order in this material breaks the mirror symmetry of the CuO$_2 bilayers. This is likely to originate from a crisscrossed arrangement of loop currents within the CuO$_2$ bilayer, resulting in a bilayer mean toroidal axis along the b direction.
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