Abstract
The discovery of the pseudogap in the cuprates1,2,3 created significant excitement as it was believed to be a signature of pairing4, in some cases above room temperature. Indeed, a number of experiments detected phase-fluctuating superconductivity above the transition temperature Tc (refs 5, 6, 7 8, 9). However, several recent experiments reported that the pseudogap and superconducting state are characterized by different energy scales10,11,12,13,14, and probably compete with each other15,16, leaving open the question of whether the pseudogap is caused by pair formation. Here we report the discovery of a spectroscopic signature of pair formation and demonstrate that in a region commonly referred to as the pseudogap, two distinct states coexist: one that is due to pair formation and persists to an intermediate temperature Tpair<T* and a second—the ‘proper’ pseudogap—characterized by the loss of spectral weight and anomalies in transport properties that extends up to T*. Tpair has a value around 120–150 K even for materials with very different Tc values and it probably sets a limit on the highest attainable Tc in the cuprates.
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Acknowledgements
We thank A. Millis, C. Varma and M. Norman for useful discussions. This work was supported by Basic Energy Sciences, US DOE. The Ames Laboratory is operated for the US DOE by Iowa State University under Contract No. W-7405-ENG-82. Work at Brookhaven is supported by the US DOE under Contract No. DE-AC02-98CH10886. J.S.W. and Z.J.X. are supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the US DOE, Office of Science.
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T.K. and A.K. designed the experiment. T.K., Y.H., T.T., J.S.W., Z.J.X. and G.G. grew the high-quality single crystals. T.K. and A.D.P. acquired the experimental data and T.K. carried out the data analysis. T.K., A.K. and J.S. wrote the manuscript. All authors discussed the results and commented on the manuscript.
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Kondo, T., Hamaya, Y., Palczewski, A. et al. Disentangling Cooper-pair formation above the transition temperature from the pseudogap state in the cuprates. Nature Phys 7, 21–25 (2011). https://doi.org/10.1038/nphys1851
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DOI: https://doi.org/10.1038/nphys1851
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