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Originally published in Science Express on 16 November 2006
Science 22 December 2006:
Vol. 314. no. 5807, pp. 1914 - 1916
DOI: 10.1126/science.1134742
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Reports

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. Gu1

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 nonsuperconducting, 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.

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 Laboratory for Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA.

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

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