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Unusual magnetic order in the pseudogap region of the superconductor HgBa2CuO4+δ


The pseudogap region of the phase diagram is an important unsolved puzzle in the field of high-transition-temperature (high-Tc) superconductivity, characterized by anomalous physical properties1,2. There are open questions about the number of distinct phases and the possible presence of a quantum-critical point underneath the superconducting dome3,4,5. The picture has remained unclear because there has not been conclusive evidence for a new type of order. Neutron scattering measurements for YBa2Cu3O6+δ (YBCO) resulted in contradictory claims of no6,7 and weak8,9 magnetic order, and the interpretation of muon spin relaxation measurements on YBCO10,11 and of circularly polarized photoemission experiments on Bi2Sr2CaCu2O8+δ(refs 12, 13) has been controversial. Here we use polarized neutron diffraction to demonstrate for the model superconductor HgBa2CuO4+δ (Hg1201) that the characteristic temperature T* marks the onset of an unusual magnetic order. Together with recent results for YBCO14,15, this observation constitutes a demonstration of the universal existence of such a state. The findings appear to rule out theories that regard T* as a crossover temperature16,17,18 rather than a phase transition temperature19,20,21. Instead, they are consistent with a variant of previously proposed charge-current-loop order19,20 that involves apical oxygen orbitals22, and with the notion that many of the unusual properties arise from the presence of a quantum-critical point3,4,5,19.

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Figure 1: Pseudogap in underdoped Hg1201.
Figure 2: Unusual magnetic order revealed by polarized-neutron diffraction.
Figure 3: Universal pseudogap phase diagram.


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We thank H. Alloul and C. Varma for comments. The work at Stanford University was supported by grants from the US Department of Energy and the National Science Foundation.

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Li, Y., Balédent, V., Barišić, N. et al. Unusual magnetic order in the pseudogap region of the superconductor HgBa2CuO4+δ. Nature 455, 372–375 (2008).

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