Emergence of Preformed Cooper Pairs from the Doped Mott Insulating State in Bi{2}Sr{2}CaCu{2}O{8+delta}
Superconductors are characterized by an energy gap that represents the energy needed to break the pairs of electrons (Cooper pairs) apart. At temperatures considerably above those associated with superconductivity, the high-transition-temperature copper oxides have an additional 'pseudogap'. It has been unclear whether this represents preformed pairs of electrons that have not achieved the coherence necessary for superconductivity, or whether it reflects some alternative ground state that competes with superconductivity. Paired electrons should display particle-hole symmetry with respect to the Fermi level (the energy of the highest occupied level in the electronic system), but competing states2, 3, 4 need not show such symmetry. Here we report a photoemission study of the underdoped copper oxide Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} that shows the opening of a symmetric gap only in the anti-nodal region, contrary to the expectation that pairing would take place in the nodal region. It is therefore evident that the pseudogap does reflect the formation of preformed pairs of electrons and that the pairing occurs only in well-defined directions of the underlying lattice.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 980187
- Report Number(s):
- BNL-93105-2010-JA; NATUAS; TRN: US1005430
- Journal Information:
- Nature (London), Vol. 456; ISSN 0028-0836
- Country of Publication:
- United States
- Language:
- English
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