Recent scanning-tunneling spectroscopy (STS) studies of the cupric oxychloride Nax Ca2-x Cu O2 Cl2 (NCCOC) have uncovered a periodic 4a×4a density of states (DOS) modulation, termed a "checkerboard". The periodicity of this phase is the same as that of the "stripe" charge order observed with neutron scattering in the very similar systems La1.48 Nd0.4 Sr0.12 Cu O4 (LNSCO) and La1.875 Ba0.125 Cu O4 (LBCO). This raises the question of whether the stripes are, in fact, actually checkerboards. Unfortunately, NCCOC samples are very small and LBCO and LNSCO samples do not cleave, so neutron and STS measurements cannot be carried out on the same system. To determine the relationship between stripes and checkers, we used resonant soft-x-ray scattering, previously applied to LBCO, to study single crystals of NCCOC. No evidence was seen for a 4a×4a DOS modulation, indicating that the checkerboard effect is not directly related to the stripe modulation in LBCO. We place an upper bound on the product of the charge amplitude and the square of the in-plane correlation length of 2.3× 103 hole Å2. Our measurements suggest that the checkers in NCCOC are either glassy or are nucleated by the surface, as suggested by Brown [Phys. Rev. B 71, 224512 (2005)].
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Feb 8 2007|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics