Issue
EPL
Volume 88, Number 2, October 2009
Article Number 27008
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/88/27008
Published online 10 November 2009
EPL, 88 (2009) 27008
DOI: 10.1209/0295-5075/88/27008

Spectroscopic evidence for preformed Cooper pairs in the pseudogap phase of cuprates

M. Shi1, A. Bendounan2, E. Razzoli1, S. Rosenkranz3, M. R. Norman3, J. C. Campuzano3, 4, J. Chang2, M. Månsson5, 6, Y. Sassa2, T. Claesson6, O. Tjernberg6, L. Patthey1, N. Momono7, M. Oda7, M. Ido7, S. Guerrero8, C. Mudry8 and J. Mesot2

1   Swiss Light Source, Paul Scherrer Institute - CH-5232 Villigen PSI, Switzerland
2   Paul Scherrer Institute, ETH Zurich and EPF Lausanne - 5232 Villigen PSI, Switzerland
3   Materials Science Division, Argonne National Laboratory - Argonne, IL 60439 USA
4   Department of Physics, University of Illinois at Chicago - Chicago, IL 60607 USA
5   Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute - CH-5232 Villigen PSI, Switzerland
6   Materials Physics, Royal Institute of Technology KTH - S-164 40 Kista, Sweden, EU
7   Department of Physics, Hokkaido University - Sapporo 060-0810, Japan
8   Condensed Matter Theory Group, Paul Scherrer Institute - CH-5232 Villigen PSI, Switzerland

ming.shi@psi.ch

received 31 July 2009; accepted in final form 6 October 2009; published October 2009
published online 10 November 2009

Abstract
Angle-resolved photoemission on underdoped La1.895Sr0.105CuO4 reveals that in the pseudogap phase, the dispersion has two branches located above and below the Fermi level with a minimum at the Fermi momentum. This is characteristic of the Bogoliubov dispersion in the superconducting state. We also observe that the superconducting and pseudogaps have the same d-wave form with the same amplitude. Our observations provide direct evidence for preformed Cooper pairs, implying that the pseudogap phase is a precursor to superconductivity.

PACS
74.72.Dn - La-based cuprates.
74.25.Jb - Electronic structure.
79.60.-i - Photoemission and photoelectron spectra.

© EPLA 2009