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تسجيل مستخدم جديدKerr effect as evidence of gyrotropic order in the cuprates - revisited
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Recent analysis has confirmed earlier general arguments that the Kerr response vanishes in any time-reversal invariant system which satisfies the Onsager relations. Thus, the widely cited relation between natural optical activity (gyrotropy) and the Kerr response, employed in Hosur textit{et al}, Phys. Rev. B textbf{87}, 115116 (2013), is incorrect. However, there is increasingly clear experimental evidence that, as argued in our paper, the onset of an observable Kerr-signal in the cuprates reflects point-group symmetry rather than time-reversal symmetry breaking.
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The Kerr effect can arise in a time-reversal invariant dissipative medium that is gyrotropic, i.e. one that breaks inversion ($mathcal I$) and all mirror symmetries. Examples of such systems include electron analogs of cholesteric liquid crystals, an
d their descendants, such as systems with chiral charge ordering. We present arguments that the striking Kerr onset seen in the pseudogap phase of a large number of cuprate high temperature superconductors is evidence of chiral charge ordering. We discuss additional experimental consequences of a phase transition to a gyrotropic state, including the appearance of a zero field Nernst effect.
The loop-current state discovered in the pseudogap phase of cuprates breaks time reversal symmetry and lowers the point group symmetry of the crystal. The order parameter and the magnetic structure within each unit cell which is associated with it ca
n be described by a toroidal moment parallel to the copper-oxide planes. We discuss lattice point group symmetry of the magnetic structure. As an application, we discuss a few effects that necessarily accompany order parameter in the pseudogap phase. The magnitude estimated for these specific effects makes them hard to observe because they rely on the small magnetic fields associated with the order parameter. Effects, associated with the electronic energies are much larger. Some of them have already been discussed.
Preformed pairs above $T_c$ and the two-gap scenarios are two main proposals for describing the low doping pseudogap phase of high-$T_c$ cuprates. Very recent angle-resolved photoemission experiments have shown features which were interpreted as evid
ence for preformed pairs. Here it is shown that those results can be explained also in the context of the two-gap scenario if self-energy effects are considered. The discussion is based on the $d$-CDW theory or the flux phase of the $t-J$ model.
X-ray absorption spectroscopy (XAS) and high resolution X-ray diffraction are combined to study the interplay between electronic and lattice structures in controlling the superconductivity in cuprates with a model charge-compensated CaxLa1-xBa1.75-xL
a0.25+xCu3Oy (0<x<0.5, y=7.13) system. In spite of a large change in Tc, the doped holes, determined by the Cu L and O K XAS, hardly show any variation with the x. On the other hand, the CuO2 plaquette size shows a systematic change due to different size of substituted cations. The results provide a direct evidence for the chemical pressure being a key parameter for controlling the superconducting ground state of the cuprates.
Angle-resolved photoemission on underdoped La$_{1.895}$Sr$_{0.105}$CuO$_4$ reveals that in the pseudogap phase, the dispersion has two branches located above and below the Fermi level with a minimum at the Fermi momentum. This is characteristic of th
e Bogoliubov dispersion in the superconducting state. We also observe that the superconducting and pseudogaps have the same d-wave form with the same amplitude. Our observations provide direct evidence for preformed Cooper pairs, implying that the pseudogap phase is a precursor to superconductivity.
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