Clocking the onset of bilayer coherence in a high- Tc cuprate

In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature TC. Here we show via a combination of far-infrared ellipsometry and ultrafast broadband optical spectroscopy that signatures of such a state can be obtained via three independent observables in an underdoped sample of NdBa2Cu3O6+δ. The pseudogap correlations were disentangled from the response of laser-broken pairs by clocking their characteristic time scales. The onset of a superconducting precursor state was found at a temperature TONS > TC, consistent with the temperature scale identified via static optical spectroscopy. Furthermore, the temperature evolution of the coherent vibration of the Ba ion, strongly renormalized by the onset of superconductivity, revealed a pronounced anomaly at the same temperature TONS. The microscopic nature of such a precursor state is discussed in terms of preformed pairs and enhanced bilayer coherence.

Published in:
Physical Review B, 95, 024501

 Record created 2018-04-23, last modified 2019-05-07

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