Department of Physics at the University of Illinois at Urbana-Champaign

First Measurement of "Static Stripe" Phase in LBCO

      

Peter Abbamonte's group has measured for the first time the charge character of the incommensurate 'static stripe' phase in La_15/8Ba_1/8CuO₄ (LBCO). Previously seen only as spin modulations in neutron scattering experiments, new studies of LBCO using resonant x-ray scattering show that the incommensurate phase also involves a significant modulation of the doped carriers. This study provides support for the electron nematic picture proposed by Eduardo Fradkin (UIUC) and co-workers [Kivelson, Fradkin, & Emery, Nature 393, 550 (1998)].

A reciprocal space map of the charge scattering from La_15/8Ba_1/8CuO₄, is shown in the upper left image. In the plot at the right, the intensity of charge scattering as the beam energy is tuned through the oxygen K edge (red) is compared with x-ray absorption data (green). The peak at 530 eV indicates significant participation of spectral weight near the Mott gap.

Resonant x-ray scattering experiments are done by carrying out x-ray diffraction with the photon energy tuned near the oxygen K edge, which involves atomic transitions directly into the valence band. By comparing with calibrated references, the Abbamonte group determined that most of the doped carriers are modulated in this phase. Experiments also observed unexpected spectral weight modulations extending all the way up to the correlated gap, showing that not just the carrier density but in fact the "Mottness," or degree to which the system also resembles a Mott insulator, is modulated in real space. These observations provide clear evidence that this phase is driven by strong coupling rather than simple Fermi surface nesting.

Currently the group is studying how stripes melt as the carrier density is tuned away from x = 1/8 and is trying to understand how to interpret resonance measurements in materials in which the stripes are said to be "fluctuating."

This work was carried out on beam line X1B, a UIUC co-run facility, at the National Synchrotron Light Source, Brookhaven National Laboratory. This work was supported by the Office of Science at the U.S. Department of Energy. The conclusions presented are those of the researchers and not necessarily those of the funding agencies.