A rare combination of strong spin–orbit coupling and electron–electron correlations makes the iridate Mott insulator Sr2IrO4 a promising host for novel electronic phases of matter1,2. The resemblance of its crystallographic, magnetic and electronic structures1,2,3,4,5,6 to La2CuO4, as well as the emergence on doping of a pseudogap region7,8,9 and a low-temperature d-wave gap10,11, has particularly strengthened analogies to cuprate high-Tc superconductors12. However, unlike the cuprate phase diagram, which features a plethora of broken symmetry phases13 in a pseudogap region that includes charge density wave, stripe, nematic and possibly intra-unit-cell loop-current orders, no broken symmetry phases proximate to the parent antiferromagnetic Mott insulating phase in Sr2IrO4 have been observed so far, making the comparison of iridate to cuprate phenomenology incomplete. Using optical second-harmonic generation, we report evidence of a hidden non-dipolar magnetic order in Sr2IrO4 that breaks both the spatial inversion and rotational symmetries of the underlying tetragonal lattice. Four distinct domain types corresponding to discrete 90°-rotated orientations of a pseudovector order parameter are identified using nonlinear optical microscopy, which is expected from an electronic phase that possesses the symmetries of a magneto-electric loop-current order14,15,16,17,18. The onset temperature of this phase is monotonically suppressed with bulk hole doping, albeit much more weakly than the Néel temperature, revealing an extended region of the phase diagram with purely hidden order. Driving this hidden phase to its quantum critical point may be a path to realizing superconductivity in Sr2IrO4.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $15.58 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
We thank S. Lovesey and D. Khalyavin for providing information about the magnetic point group of the Néel order in Sr2IrO4. We acknowledge useful discussions with P. Armitage, L. Fu, A. Kaminski, P. A. Lee, O. Motrunich, J. Orenstein, N. Perkins, S. Todadri, C. Varma and V. Yakovenko. This work was support by ARO Grant W911NF-13-1-0059. Instrumentation for the SHG measurements was partially supported by ARO DURIP Award W911NF-13-1-0293. D.H. acknowledges funding provided by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center (PHY-1125565) with support of the Gordon and Betty Moore Foundation through Grant GBMF1250. R.F. acknowledges the hospitality of the Aspen Center for Physics, supported by NSF Grant PHYS-1066293, where some of this work was carried out. G.C. acknowledges NSF support via Grant DMR-1265162. R.L. acknowledges support from the Israel Science Foundation through Grant 556/10.
About this article
Nature Communications (2017)