Photoemission Evidence for a Remnant Fermi Surface and a d-Wave-Like Dispersion in Insulating Ca$_2$CuO$_2$Cl$_2

• Published in: Science (American Association for the Advancement of Science) Vol. 282; no. 5396; pp. 2067 - 2072
• Main Authors: Ronning, F., Kim, C., Feng, D. L., Marshall, D. S., Loeser, A. G., Miller, L. L., Eckstein, J. N., Bozovic, I., Z.-X. Shen
• Format: Journal Article
• Language: English
• Published: American Society for the Advancement of Science 11-12-1998
• Subjects: Contour lines; Correlations; Doping; Electrons; Fermi surfaces; Isoenergetic processes; Liquids; Photoelectric emission; Superconductors; Surface contours
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.282.5396.2067

An angle-resolved photoemission study is reported on Ca$_2$CuO$_2$Cl$_2$, a parent compound of high-T$_c$ superconductors. Analysis of the electron occupation probability, n(k), from the spectra shows a steep drop in spectral intensity across a contour that is close to the Fermi surface predicted by the band calculation. This analysis reveals a Fermi surface remnant, even though Ca$_2$CuO$_2$Cl$_2$ is a Mott insulator. The lowest energy peak exhibits a dispersion with approximately the ǀcosk$_x$a - cosk$_y$aǀ form along this remnant Fermi surface. Together with the data from Dy-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, these results suggest that this d-wave-like dispersion of the insulator is the underlying reason for the pseudo gap in the underdoped regime.