Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states
M. J. Lawler, K. Fujita, Jhinhwan Lee, A. R. Schmidt, Y. Kohsaka, Chung Koo Kim, H. Eisaki, S. Uchida, J. C. Davis, J. P. Sethna & Eun-Ah Kim
Nature 466, 347–351 (15 July 2010) doi:10.1038/nature09169
Received 05 March 2010
Accepted 04 May 2010
In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced1. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within each CuO2 unit cell. We analyse spectroscopic-imaging scanning tunnelling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8 + δ and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90°-rotational symmetry within every CuO2 unit cell.
Figure 1: CuO2 electronic structure and ω ≈ Δ1 pseudogap states.
CuO2 electronic structure and [ohgr][thinsp][ap][thinsp][Dgr]1 pseudogap states.
a, Schematic of the spatial arrangements of CuO2 electronic structure with Cu sites and orbitals indicated in blue and O sites and 2pσ orbitals in yellow. EF, Fermi energy. The inset shows the approxi…
Figure 2: Imaging the spatial symmetries of the ω ≈ Δ1 pseudogap states.
Imaging the spatial symmetries of the [ohgr][thinsp][ap][thinsp][Dgr]1 pseudogap states.
a, Spatial image (R-map5) of the Bi2Sr2CaCu2O8 + δ pseudogap states ω ≈ Δ1 at T ≈ 4.3 K for an underdoped sample with Tc = 35 K. The inset shows the Fourier transform upon which the inequivalent Bragg vectors Qx = (1, 0)2π/a0 and Qy =…
Figure 3: Nematic ordering and O-site specificity of ω ≈ Δ1 pseudogap states.
Nematic ordering and O-site specificity of [ohgr][thinsp][ap][thinsp][Dgr]1 pseudogap states.
a, Topographic image T(r) of the Bi2Sr2CaCu2O8 + δ surface. The inset shows that the real part of its Fourier transform ReT(q) does not break C4 symmetry at its Bragg points because plots of T(q) show its values to be indistinguishable…
Figure 4: Rapid increase of correlation length of nematicity at ω ≈ Δ1.
Rapid increase of correlation length of nematicity at [ohgr][thinsp][ap][thinsp][Dgr]1.
a, A large FOV T(r) image which preserves C4 symmetry. b, Correlation lengths for the nematic ordering (red solid diamonds), and f…