Density Wave Probes Cuprate Quantum Phase Transition

May 3, 2019

Cuprates—materials based on copper and oxygen—have been intensely studied for over three decades because of their high-temperature superconducting properties. Attempts to understand these properties have exposed an even larger set of novel behaviors that challenge the conventional framework of condensed-matter physics. Thus, it has become pressing to find and understand the connection between these exotic states. Using scanning tunneling microscopy, we image spatial patterns of modulated electron density as a fingerprint of the underlying organization. We discover a transition in the modulations coincident with the sudden appearance of more conventional metallic properties. These observations point to an underlying set of electronic interactions that control the exotic behaviors.

Tuning the states in cuprates is achieved by doping: removing electrons from the copper-oxygen lattice. At one doping extreme, the electronic behavior is insulating, while at the other extreme it is metallic. In a conventional metal, the momenta of electrons at zero energy form a closed contour called the Fermi surface. One of the biggest mysteries in cuprate research is the existence of open arcs rather than a conventional Fermi surface at low doping.

Doping varies spatially within cuprates, giving rise to local changes in electronic structure. In a paper published in Physical Review X, physics graduate student Tatiana A.Webb, members of Prof. Jenny Hoffman's lab, and colleagues from MIT, Nagoya University, and Penn State describe imaging these local variations to provide a detailed characterization of the evolution of both the Fermi surface and charge modulations. At a single doping, the charge modulations lock onto the crystal lattice, becoming commensurate, and the Fermi surface simultaneously transforms into arcs.

This link between Fermi-surface structure and charge modulations suggests a common underlying mechanism controlling both phenomena, opening opportunities for further investigations of the nature of the states on both sides of the transition.

Read T.A. Webb, M.C. Boyer, Y. Yin, D. Chowdhury, Y. He, T. Kondo, T. Takeuchi, H. Ikuta, E.W. Hudson, J.E. Hoffman, and M.H. Hamidian, "Density Wave Probes Cuprate Quantum Phase Transition," Phys. Rev. X 9 (1 May 2019) https://doi.org/10.1103/PhysRevX.9.021021.