Density Wave with d-Form Factor an Answer to the Mysterious Pseudogap?

This week, Seamus Davis, a leader in the field of scanning tunneling microscopy (STM) was in town and gave a series of talks on the many materials examined in his laboratory by his various students and postdocs. The most compelling of the talks was presented on the pseudogap phase of the high-temperature cuprate superconductors.

According to Davis, the mysterious nature of the pseudogap phase is due to the presence of a density wave with d-form factor, pictured below. In the topographic STM images of BSCCO and NaCCOC, one can see a vivid visual representation of this density wave (link to the paper PDF!).

Because STM is a surface sensitive probe, the high-Tc community always had niggling doubts about whether this density wave was manifest in the bulk. With increasing evidence that there is a density wave in the bulk from scattering probes such as resonant soft X-ray scattering and from hard x-ray diffraction, the interpretation put forth by Davis seems more plausible than it did a decade ago.

He also claimed in this talk that the presence of this density wave could explain the existence of Fermi arcs seen using angle-resolved photoemission, another surface sensitive technique. However, the observation of quantum oscillations in the underdoped cuprates demonstrating pockets at the Fermi surface complicates matters somewhat. For these two observations to be consistent, the only possible explanation is a phase transition in the underdoped cuprates as a function of magnetic field in the region of ~20 Tesla.

Nonetheless, Davis’ group has done a wonderful set of experiments on these compounds and his talks this week were captivating and enjoyable. This seems like a valuable contribution into the ongoing discussion of the mystery of the pseudogap.

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6 responses to “Density Wave with d-Form Factor an Answer to the Mysterious Pseudogap?

  1. “the only possible explanation is a phase transition in the underdoped cuprates as a function of magnetic field in the region of ~20 Tesla”
    U know what? It even exists…
    http://www.nature.com/nature/journal/v477/n7363/full/nature10345.html
    http://www.nature.com/ncomms/2013/130703/ncomms3113/full/ncomms3113.html
    http://www.nature.com/nphys/journal/v9/n2/full/nphys2502.html

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    • Thank you for the links! I finally got around to reading the papers. I am a little confused on one point and perhaps you can illuminate me: Davis seemed to indicate that the density wave existed in the pseudogap state and essentially was the same structure seen in X-ray studies (RSXS and XRD). The papers you attached seem to show the existence of a charge ordered phase that is seemingly non-existent in the absence of magnetic field. Of course there is some charge order without magnetic fields as has been seen in YBCO by Blackburn et al among others. So what exactly is the nature of the transition? Is it from a short correlation length charge ordered state to a longer-range order charge order state?

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  2. Pingback: Was the Higgs Boson Discovered in 1980? | This Condensed Life

  3. This is indeed a good question. I don’t think anyone has a definitive answer at the moment. Clearly, there are two different “phases” (both are seen by NMR but X-ray studies have only detected the zero/low-field one so far), and indeed the high-field phase must have a large correlation length. See the recent discussion here: see http://dx.doi.org/10.1038/ncomms7438.

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    • http://www.nature.com/nphys/journal/v8/n12/full/nphys2456.html

      Putting together the observations in the paper above with the NMR studies you have linked seems like evidence that perhaps the X-rays are seeing a fluctuating short-ranged version of the NMR-observed charge order.

      Unfortunately, this cannot be proven just yet though, as the X-ray studies have not reached the magnetic fields attained in the NMR studies. It is suggestive that the two observations are seeing similar phenomena, though. Thanks again for the links. Very interesting indeed!

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  4. According to http://dx.doi.org/10.1038/ncomms7438, what X-rays are seeing must be static static because it is already static for NMR. However, it is possible (but not proven) that it would be fluctuating in the absence of disorder. The NMR paper above argues that there are two CDW modulations, one long-ranged in high fields and low T, the other short-ranged everywhere (meaning they coexist).
    Now, check this out! http://arxiv.org/abs/1506.07910

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