Commensurate antiferromagnetic excitations as a signature of the pseudogap in the tetragonal high-Tc cuprate HgBa${}_2$CuO${}_{4+\hat{I}´}$

Abstract

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 HgBa${}_2$CuO${}_{4+\hat{I}´}$. Here we report neutron scattering results for HgBa${}_2$CuO${}_{4+\hat{I}´}$ (superconducting transition temperature T${}_c$ $\sim$ 71 K, pseudogap temperature T* $\sim$ 305 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.