paper

Clocking the Onset of Bilayer Coherence in a High- Cuprate

arXiv:1510.00305 · doi:10.1103/PhysRevB.95.024501

Abstract

In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature . 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 NdBaCuO. 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 , 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 . The microscopic nature of such a precursor state is discussed in terms of pre-formed pairs and enhanced bilayer coherence.

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