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It may simply be the result of the anisotropy in the thermal conductivity tensor. This point is especially relevant when the thermal Hall response is measured with the magnetic field applied parallel to the CuO2 plane. [31] Millis A J, Monien H and Pines D 1990 Phys. Rev. B 42 167 [32] Abanov A, Chubukov A V and Schmalian J 2003 Adv. Phys. 52 119 [33] Berg E, Metlitski M A and Sachdev S 2012 Science 338 1606 [34] Li Tao 2018 arXiv:1805.06395 [35] Li T and Yao D W 2020 J. Phys.: Condens. Matter 33 095601 [36] While a full answer to these questions still await future works, we note that the quantum critical behavior at x = xc may be explained without invoking symmetry breaking phase transition if we assume that the local moment system (which is assumed to be far from critical but is otherwise antiferromagnetically correlated) is coupled to a quasiparticle system with a divergent antiferromagentic susceptibility. The latter is true because the Van Hove singularity and the antiferromagnetic hot spot coincide on the Fermi surface when x = xc.[34] [37] Here what concern us are those spectral anomalies that are beyond the description of the low energy effective theory. The local–itinerant dualism of electron in the high-Tc cuprates is the most important origin for such spectral anomalies at the intermediate to high energy range, for example, the waterfall structure and the prominent particle–hole asymmetry in the single particle spectrum, the ubitoqus non-Drude behavior in the optical conductivity spectrum, the Raman spectrum and the charge fluctuation spectrum, and the high energy continuum in the spin fluctuation spectrum which is up to now still poorly understood as a result of the limitation in the measurement resolution. [38] Many previous studies have focused on the search of a ’paring glue’ from the emergent degree of freedom at low energy, such as the neutron resonance mode, but have forgotten the fact that such emergent degree of freedom appears on the background of anomalous dynamics at the intermediate to high energy range, which may have a closer relation with the mechanism of superconductivity in the high-Tc cupartes. A more detailed analysis on this point can be found in Ref.[35]. |