Charge density wave memory in a cuprate superconductor

Abstract

Although CDW correlations are a ubiquitous feature of the superconducting cuprates, their disparate properties suggest a crucial role for pinning the CDW to the lattice. Here, we report coherent resonant X-ray speckle correlation analysis, which directly determines the reproducibility of CDW domain patterns in La 1.875 Ba 0.125 CuO 4 (LBCO 1/8) with thermal cycling. While CDW order is only observed below 54 K, where a structural phase transition creates inequivalent Cu-O bonds, we discover remarkably reproducible CDW domain memory upon repeated cycling to far higher temperatures. That memory is only lost on cycling to 240(3) K, which recovers the four-fold symmetry of the CuO 2 planes. We infer that the structural features that develop below 240 K determine the CDW pinning landscape below 54 K. This opens a view into the complex coupling between charge and lattice degrees of freedom in superconducting cuprates.

Distinction between pristine and disorder-perturbed charge density waves in ZrTe3

“…Hence, we do not think a direct analogy between the CDWs (and the FOs) in ZrTe 3 and the cuprates should be drawn at this point. Yet empirically, it does seem that even the rather long-range CDWs studied recently in La 1:875 Ba 0:125 CuO 4 lack the phenomena that we have seen: only one peak (considerably broader than ours) and one characteristic temperature were observed, and the speckle patterns were found to be always static at low temperatures 33 and with memory effects up to high temperatures 46 . The counterpart of our finding, namely, the role of disorder in charge-order formation in the strong-coupling limit, to which the cuprates belong, deserves further experimental scrutiny.…”

Domain Texture of the Orthorhombic Phase of La2−xBaxCuO4

“…The method described in the "Domain Counting Argument" section above, informs us that, within the 1.4-μm sphere, there are roughly five domains across the transverse direction and two along the (012) radial direction. Therefore, the LTO domains, roughly 280 nm wide and 700 nm long, correspond well to the estimates made from the incoherent envelope of the 3D diffraction pattern, as used for the estimates made in our previous publication [15]. An a-b anisotropy within the orthorhombic phase was observed before in c-axis darkfield transmission electron microscope (TEM) images, with roughly the same dimensions [25,26].…”

“…1, showing the crosscorrelation (defined below) of a region of the speckled diffraction pattern measured at 24 K before and after cycling up to the designated upper temperature, T cycle , and back. As can be clearly seen, the speckles remain highly correlated all the way up to T LTO = 240 K. Only after cycling the temperature above the higher orthorhombic transition temperature, T LTO , did the pattern of speckles, hence domains, rearrange [15].…”

“…Our previous experiments on LBCO [13,14] used soft coherent X-ray diffraction to study the speckle pattern generated by the CDW domains at 10 K. It was found firstly that the speckles were static over long periods [13], hence that the domain texture does not fluctuate, and secondly that the speckle positions were stable in temperature, even as the material was thermally cycled above the T LTT phase transition where the CDWs melt and the diffraction signal disappears [15]. This result is summarized in Fig.…”

“…The important conclusion of that work [15] was that the CDW domains are pinned by the structural domains that form at the LTO phase transition. When the temperature was raised above T LTO and cooled down again, a different configuration of LTO domains was formed and that led to a different pinning pattern of the CDW domains when the CDW formed again below T LTT .…”