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Published Online November 16, 2006
Science DOI: 10.1126/science.1134742

Reports

Submitted on September 5, 2006
Accepted on November 3, 2006

The Ground State of the Pseudogap in Cuprate Superconductors

T. Valla 1*, A. V. Fedorov 2, Jinho Lee 3, J. C. Davis 3, G. D. Gu 1

1 Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
3 LASSP, Department of Physics, Cornell University, Ithaca, NY 14850, USA.

* To whom correspondence should be addressed.
T. Valla , E-mail: valla{at}bnl.gov

We present studies of the electronic structure of La2-xBaxCuO4, a system where the superconductivity is strongly suppressed as static spin and charge orders or 'stripes' develop near the doping level of x=1/8. Using angle-resolved photoemission and scanning tunneling microscopy, we detect an energy gap at the Fermi surface with magnitude consistent with d-wave symmetry and with linear density of states, vanishing only at four nodal points, even when superconductivity disappears at x=1/8. Thus, the non-superconducting, 'striped' state at x=1/8 is consistent with a phase incoherent d-wave superconductor whose Cooper pairs form spin/charge ordered structures instead of becoming superconducting.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)