https://doi.org/10.1140/epjst/e2010-01298-7
Review
Pseudogap and precursor superconductivity in underdoped cuprate high temperature superconductors: A far-infrared ellipsometry study
1 Department of Physics and Fribourg Center for Nanomaterials, University of Fribourg, Chemin du Musée 3, 1700 Fribourg, Switzerland
2 Institute of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic
3 Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany
4 Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
a Actual address: National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, PO Box 603, Beijing 100190, Peoples Republic of China
b e-mail: christian.bernhard@unifr.ch
Received:
14
July
2010
Revised:
12
August
2010
Published online:
11
October
2010
With the technique of infrared ellipsometry we performed a detailed study of the temperature- and doping dependence of the c-axis response of a series of YBa2Cu3O7−δ single crystals. In particular, we explored the anomalous electronic properties at temperatures above the macroscopic superconducting transition temperature, Tc, whose conflicting explanations range from a precursor superconducting state to electronic correlations that compete with superconductivity. We show that the c-axis spectra provide evidence that both kinds of correlations are present and that their contributions can be disentangled based on an analysis with a so-called multilayer-model. We find that the onset temperature, T*, and the energy scale, ΔPG, of the competing pseudogap increase rapidly towards the underdoped side whereas they vanish on the overdoped side. In addition, we provide evidence that in a strongly underdoped sample the precursor superconducting correlations develop below an onset temperature, Tons, that is considerably lower than T* but still much higher than Tc.
© EDP Sciences, Springer-Verlag, 2010
