Abstract
While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wave vectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here, we investigate the temperature dependence of the low-energy phonons in the canonical CDW-ordered cuprate . We discover that the phonon softening wave vector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wave vector of 0.238 reciprocal lattice units (r.l.u.) below the ordering transition temperature to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that “214”-type cuprates can host CDW correlations at a similar wave vector to previously reported CDW correlations in non-214-type cuprates such as . This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.
- Received 4 May 2017
- Revised 25 November 2017
DOI:https://doi.org/10.1103/PhysRevX.8.011008
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
In most metals, the itinerant free electrons are spread uniformly throughout the material. But in some substances, such as high-temperature superconductors (HTSCs), the electrons can form standing waves known as charge density waves (CDWs), which deform the underlying atomic crystal lattice of the material. In 2012, researchers discovered this electronic state in the HTSC , triggering intense debate about whether this behavior has the same origin as charge correlations discovered in another HTSC family, , over 20 years ago. Here, we examine the CDW correlations in through its interaction with collective lattice motions and find strong evidence to support a unified CDW mechanism in high-temperature superconductors.
We use state-of-the-art x-ray techniques to precisely measure the lattice vibrations in and find how they couple to the CDW. We discovered that the fluctuating CDW correlations that exist at high temperature have a different periodicity than the static ordered CDW but the same periodicity as , which may arise from coupling between the CDW and spin correlations. This reconciles the puzzling wave-vector difference between and , thus providing strong evidence that CDWs in different cuprates are likely to arise from the same underlying instability despite their different ordering wave vectors.
Our results provide a vital new characterization of the electronic state from which high-temperature superconductivity emerges.