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Louis Taillefer - Université de Sherbrooke, Canada

Fermi Surface reconstruction and nematicity in cuprate superconductors

Quantum oscillations and negative Hall and Seebeck coefficients at low temperature and high magnetic field have shown the Fermi surface of underdoped cuprates to contain a small closed electron pocket [1]. It is thought to result from a reconstruction by charge order, but whether it is the order seen by NMR and ultrasound above a threshold field or the short-range modulations seen by X-ray diffraction in zero field is unclear. We have used measurements of the thermal Hall conductivity in YBa2Cu3Oy [2] inside the superconducting state to answer this question.

In parallel, nematicity has emerged as a key feature of cuprate superconductors, but its link to charge order and the pseudogap remains unclear. We have used measurements of transport anisotropy in YBa2Cu3Oy to distinguish two sources of anisotropy : one associated with charge modulations and another associated with the pseudogap [3]. In the second case, the onset of in-plane anisotropy follows a line in the temperature-doping phase diagram that tracks the pseudogap energy. This nematic line decreases with doping until it hits the dome of charge order at its summit. It also hits the dome of superconductivity at its summit, once the competing effect of charge order has been suppressed by pressure [4]. This is compelling evidence for a pseudogap phase with nematic character that shapes the domes of both superconductivity and charge order.

[1] N. Doiron-Leyraud et al., Nature Communications 6, 6034 (2015).

[2] G. Grissonnanche et al., arXiv:1503.07572 (2015).

[3] O. Cyr-Choinière et al., arXiv:1504.06972 (2015).

[4] O. Cyr-Choinière et al., arXiv:1503.02033 (2015).


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