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Loop Currents in Superconducting Cuprates and Iridates - Philippe Bourges

CEA Saclay

LPS Bât 510 Moyen Amphi

There has been a long-standing debate among condensed-matter physicists about the origin of the pseudo-gap state in high-temperature superconducting cuprates. Polarized neutron diffraction has revealed the existence of an ordered magnetic phase, hidden inside the pseudo-gap state of underdoped YBa2Cu3O6+x, HgBa2CuO4+d and Bi2Sr2CaCu2O8+d [1]. Interestingly, the ordering temperature matches the pseudo-gap temperature T* deduced from resistivity measurements. The magnetic order can be described as an Intra-Unit-cell magnetic order, breaking time-reversal and C4 rotational symmetries. It corresponds to the symmetry predicted in the loop current theory of the pseudo-gap state where staggered current loops give rise to orbital-like magnetic moments within the CuO2 unit cell. I will review these observations in light of the loop current model. Other proposals, based on magneto-electric quadrupoles, will be presented as well. Recently, we observed similar magnetic signal in the antiferromagnetic iridates system Sr2(Ir,Rh)O4 [2] below a temperature different from TN suggesting the existence of loop-current electronic states in different oxides.

collaborators : Lucile Mangin-Thro, Jaehong Jeong, Yvan Sidis (LLB-Orphée), Yuan Li (Peking University), Yang Tang, Martin Greven (Minnesota University),Véronique Brouet (LPS Orsay) .
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