Angular Fluctuations of a Multicomponent Order Describe the Pseudogap of YBa2Cu3O6+x

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Science  21 Mar 2014:
Vol. 343, Issue 6177, pp. 1336-1339
DOI: 10.1126/science.1246310

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The Cuprate Pseudogap

The properties of copper-oxide superconductors are changed by chemical doping, but, if doping is suboptimal, the transition temperature Tc drops. Conversely, the so-called pseudogap, a depression in the density of states around the Fermi level that may or may not be related to superconductivity, gains strength. The cuprate YBa2Cu3O6+x shows a charge density order that grows as Tc is approached from both low and high temperatures. Hayward et al. (p. 1336) have developed a model in which classical fluctuations of a six-component order parameter, encompassing both superconducting and charge orders, reproduce the characteristic concave temperature dependence of the x-ray scattering intensity and thus provide a framework for the understanding of the pseudogap regime.


The hole-doped cuprate high-temperature superconductors enter the pseudogap regime as their superconducting critical temperature, Tc, falls with decreasing hole density. Recent x-ray scattering experiments in YBa2Cu3O6+x observe incommensurate charge-density wave fluctuations whose strength rises gradually over a wide temperature range above Tc, but then decreases as the temperature is lowered below Tc. We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a six-dimensional space. The theory provides a natural quantitative fit to the x-ray data and can be a basis for understanding other characteristics of the pseudogap.

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