Nature 382, 51 - 54 (04 July 1996); doi:10.1038/382051a0

Spectroscopic evidence for a pseudogap in the normal state of underdoped high-T_c superconductors

H. Ding^*†, T. Yokoya^‡, J. C. Campuzano^*†, T. Takahashi^‡, M. Randeria^§, M. R. Norman^†, T. Mochiku^¶, K. Kadowaki^¶ & J. Giapintzakis^£

^* Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
^† Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
^‡Department of Physics, Tohoku University, Sendai 980, Japan
^§Tata Institute of Fundamental Research, Bombay 400005, India
Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
^¶ National Research Institute for Metals, Tsukuba, Ibaraki 305, Japan
^£ Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

IT is well known that BCS mean-field theory is remarkably successful in describing conventional superconductors. A central concept of BCS theory is the energy gap in the electronic excitation spectrum below the superconducting transition temperature, T _c. The gap also serves as the order parameter: quite generally, long-range phase coherence and a non-zero gap go hand-in-hand¹. But in underdoped high-T _c superconductors there is considerable evidence that a pseudogap (a suppression of spectral weight) is already formed in the normal state above T _c—first, from studies of the spin excitation spectrum^2–5,24, which measure a 'spin gap', and later from a variety of other probes^6–10. Here we present a study of underdoped Bi₂Sr₂CaCu₂O₈₊ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), which directly measures the momentum-resolved electron excitation spectrum of the CuO₂ planes. We find that a pseudogap with d-wave symmetry opens up in the normal state below a temperature T ^* > T _c, and develops into the d-wave superconducting gap once phase coherence is established below T _c.

References

1.	Schrieffer, J. R. Theory of Superconductivity (Cummings, Reading, 1964).
2.	Warren, W. W. Jr et al. Phys. Rev. Lett. 62, 1193−1196 (1989). | Article | PubMed | ISI | ChemPort |
3.	Takigawa, M. et al. Phys. Rev. B43, 247−257 (1991). | ChemPort |
4.	Alloul, H., Mahajan, A., Casalta, H. & Klein, O. Phys. Rev. Lett. 70, 1171−1174 (1993). | Article | PubMed | ChemPort |
5.	Rossat-Mignod, J. et al. Physica B186−188, 1−8 (1993).
6.	Homes, C. C., Timusk, T., Liang, R., Bonn, D. A. & Hardy, W. N. Phys. Rev. Lett. 71, 1645−1648 (1993). | Article | PubMed | ISI | ChemPort |
7.	Basov, D. N., Mook, H. A., Dabrowski, B. & Timusk, T. Phys. Rev. B52, 13141−13144 (1995).
8.	Loram, J. W., Mirza, K. A., Cooper, J. R. & Liang, W. Y. Phys. Rev. Lett. 71, 1740−1743 (1993). | Article | PubMed | ChemPort |
9.	Tallon, J. L., Cooper, J. R., de Silva, P., Williams, G. V. M. & Loram, J. W. Phys. Rev. Lett. 75, 4114−4117 (1995). | Article | PubMed | ChemPort |
10.	Batlogg, B. et al. Physica C235−240, 130−133 (1994).
11.	Ding, H. et al. Phys. Rev. Lett. 74, 2784−2787 (1995); 75, 1425 (1995). | Article | ChemPort |
12.	Shen, Z.-X. et al. Phys. Rev. Lett. 70, 1553−1556 (1993). | Article | PubMed | ISI | ChemPort |
13.	Norman, M. R., Randeria, M., Ding, H., Campuzano, J. C. & Bellman, A. F. Phys. Rev. B52, 15107−15110 (1995). | ChemPort |
14.	Ding, H. et al. http://xxx.lanl.gov/archive/cond-mat/9603044.
15.	Randeria, M. et al. Phys. Rev. Lett. 74, 4951−4954 (1995). | Article | PubMed | ISI | ChemPort |
16.	Ding, H. et al. Phys. Rev. Lett. 76, 1533−1536 (1996). | Article | PubMed | ISI | ChemPort |
17.	Loeser, A. G., Shen, Z.-X. & Dessau, D. S. Physica C263, 208−213 (1996). | ChemPort |
18.	Loeser, A. G. Science (in the press).
19.	Loram, J. W., Mirza, K. A., Wade, J. M., Cooper, J. R. & Liang, W. Y. Physica C235−240, 134−137 (1994).
20.	Randeria, M., Trivedi, N., Moreo, A. & Scalettar, R. T. Phys. Rev. Lett. 69, 2001−2004 (1992). | Article | PubMed | ISI |
21.	Trivedi, N. & Randeria, M. Phys. Rev. Lett. 75, 312−315 (1995). | Article | PubMed | ISI | ChemPort |
22.	Emery, V. & Kivelson, S. A. Nature 374, 434−437 (1995). | Article | ISI | ChemPort |
23.	Groen, W. A., de Leeuw, D. M. & Feiner, L. F. Physica C165, 55−61 (1990). | ChemPort |
24.	Imai, J. et al. Physica C162−164, 169−170 (1989).