# Hidden magnetic excitation in the pseudogap phase of a high-Tc superconductor

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Abstract : The elucidation of the pseudogap phenomenon of the high-transition-temperature (high-T$_c$) copper oxides $-$a set of anomalous physical properties below the characteristic temperature T* and above T$_c$$-$ has been a major challenge in condensed matter physics for the past two decades. Following initial indications of broken time-reversal symmetry in photoemission experiments, recent polarized neutron diffraction work demonstrated the universal existence of an unusual magnetic order below T* . These findings have the profound implication that the pseudogap regime constitutes a genuine new phase of matter rather than a mere crossover phenomenon. They are furthermore consistent with a particular type of order involving circulating orbital currents, and with the notion that the phase diagram is controlled by a quantum critical point. Here we report inelastic neutron scattering results for HgBa$_2$CuO$_{4+ \delta}$ that reveal a fundamental collective magnetic mode associated with the unusual order, and which further support this picture. The mode's intensity rises below the same temperature T* and its dispersion is weak, as expected for an Ising-like order parameter. Its energy of 52-56 meV renders it a new candidate for the hitherto unexplained ubiquitous electron-boson coupling features observed in spectroscopic studies
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Journal articles

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### Citation

Yuan Li, V. Balédent, G. Yu, N. Barišić, K. Hradil, et al.. Hidden magnetic excitation in the pseudogap phase of a high-Tc superconductor. Nature, Nature Publishing Group, 2010, 468 (7321), pp.283-285. ⟨10.1038/nature09477⟩. ⟨cea-00904213⟩

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