Abstract
The nature and behaviour of electronic states in high-temperature superconductors are the centre of much debate. The pseudogap state, observed above the superconducting transition temperature, Tc, is seen by some as a precursor to the superconducting state. Others view it as a competing phase. Recently, this discussion has focused on the number of energy gaps in the system. Some experiments indicate a single energy gap, implying that the pseudogap is a precursor state. Others indicate two, suggesting that it is a competing or coexisting phase. Here, we use temperature-dependent scanning tunnelling spectroscopy of (Bi1−yPby)2Sr2CuO6+x to clarify the situation. We find a previously unobserved narrow and homogeneous gap that vanishes near Tc, superimposed on the typically observed inhomogeneous and broad gap, which is only weakly temperature dependent. These results not only support the two-gap picture, but also explain previously troubling differences between scanning tunnelling microscopy and other experimental measurements.
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Acknowledgements
We thank J. C. Davis, J. E. Hoffman, P. A. Lee, Y. S. Lee, K. McElroy, T. Senthil, Y. Wang and X.-G. Wen for comments. This research was supported in part by a Cottrell Scholarship awarded by the Research Corporation, by the MRSEC program of the NSF under award DMR 02-13282, and also by NSF CAREER award DMR-034891.
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M.C.B., W.D.W. and K.C. shared equal responsibility for all aspects of this project from instrument construction to data collection and analysis. M.Y. conceived the temperature-normalization scheme and carried out much of the data analysis. T.K. grew the samples and helped refine the STM. T.T. and H.I. contributed to sample growth. E.W.H. advised.
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Boyer, M., Wise, W., Chatterjee, K. et al. Imaging the two gaps of the high-temperature superconductor Bi2Sr2CuO6+x. Nature Phys 3, 802–806 (2007). https://doi.org/10.1038/nphys725
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DOI: https://doi.org/10.1038/nphys725
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