Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO4+δ. Here we report neutron-scattering results for HgBa2CuO4+δ (superconducting transition temperature TcE71 K, pseudogap temperature T∗E305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: The X-shaped 'hourglass' response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped and significantly enhanced below T∗, and hence a prominent signature of the pseudogap state.
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We acknowledge fruitful discussions with Yuan Li and Chandra Varma. We thank A. Kreyssig and A.I. Goldman, C.L. Broholm and S. Koopayeh for assistance with crystal alignment work partially performed at Ames Laboratory and at the IQM at Johns Hopkins University. The work at the University of Minnesota was supported by the US Department of Energy, Office of Basic Energy Sciences, under Award No. DE-SC0006858. Research conducted at ORNL’s High-Flux Isotope Reactor and Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, the US Department of Energy. M.K.C. is supported by funds from the US Department of Energy BES grant no. LANLF100. Work at the IQM was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award DE-FG02-08ER46544. We also acknowledge financial support at LLB from the projects UNESCOS (contract ANR-14-CE05-0007) and NirvAna (contract ANR-14-OHRI-0010) of the ANR.