This project encompasses the study of the charge-order phenomenology in single-layer Bi-based high-temperature cuprate superconductors under the application of uniaxial strain. This collaborative effort will bring together the expertise of the groups of A. Damascelli, G.A. Sawatzky (QMI-UBC, Vancouver), and B. Keimer (MPI-FKF, Stuttgart), experts in the field of charge-order in cuprates.
A comprehensive description of the phase-diagram of cuprates remains one of the greatest challenges in condensed matter physics. In fact, the interplay between intertwined orders  precludes a fundamental understanding of the underlying physics. In the recently reported charge-order (CO) phase, electrons self-organize in periodic patterns breaking the translational symmetry of the crystal. CO and its interplay with other coexisting phases (mainly superconductivity) have been extensively investigated in the last few years. However, it is still unclear (i) whether CO is universally bi- or uni-directional, (ii) what is the fundamental origin of CO (i.e., stemming from strong-electronic correlations and/or quantum criticality), and (iii) how CO competes microscopically with the high-temperature superconducting phase.
In this project we will use uniaxial (tensile and compressive) strain as a tunable knob to manipulate the phase-diagram of Bi2Sr2CuO4+δ (Bi2201), in an effort to solve this long-standing puzzle. A custom-made strain device will be utilized in resonant x-ray scattering measurements to be performed at synchrotron-based facilities, including the Canadian Light Source (CLS). Resonant x-ray scattering will be used for detecting the order parameter and correlation length of the CO under strain .
The charge order has been firstly observed in La-based cuprates in terms of commensurate spin and charge stripes [3,4]. Since 2012, incommensurate CO has been reported in Y- and Bi-based cuprates [5-8], Hg-compounds , as well as electron-doped cuprates [10,11], demonstrating the ubiquity of the CO phase in cuprates. At ambient conditions, the incommensurate CO is short-range (correlation length around 20 Å in Bi2201), and purely two-dimensional. However, measurements in the presence of high-magnetic fields have reported the development of a long-range CO . More recently, measurements under uniaxial strain  and biaxial epitaxial strain  in B. Keimer’s group at MPI-FKF in collaboration with A. Mackenzie’s group at MPI-CPfS have shown the formation of three-dimensional CO in Y-based cuprates.
In this project, we will explore the generality of the three-dimensional CO-ordered state in the cuprates. The short-range CO in Bi2201 can be detected via resonant x-ray scattering measurements, as shown in Figure 1. The collaborative team led by A. Damascelli, G.A. Sawatzky (QMI-UBC), and B. Keimer (MPI-FKF) will develop and install at the REIXS Beamline at CLS mechanical and piezo-based devices for the application of strain in ultra-high-vacuum. The intensity and correlation length of the CO peaks – within the full three-dimensional momentum space – will be tracked, offering novel perspectives on the fundamental microscopic mechanisms of this quantum phase. We note that (strain-induced) long-range CO may dramatically affect the Fermi surface topology. To this end, angle-resolved photoemission spectroscopy (ARPES) measurements will be performed in Vancouver (A. Damascelli’s group at QMI-UBC), and will be combined with x-ray data in an effort to provide a comprehensive picture of how the low-energy electronic structure may be affected by strain-induced CO.