Incipient charge order observed by NMR in the normal state of YBa2Cu3Oy

Abstract

The pseudogap regime of high-temperature cuprates harbours diverse manifestations of electronic ordering whose exact nature and universality remain debated. Here, we show that the short-ranged charge order recently reported in the normal state of YBa2Cu3Oy corresponds to a truly static modulation of the charge density. We also show that this modulation impacts on most electronic properties, that it appears jointly with intra-unit-cell nematic, but not magnetic, order, and that it exhibits differences with the charge density wave observed at lower temperatures in high magnetic fields. These observations prove mostly universal, they place new constraints on the origin of the charge density wave and they reveal that the charge modulation is pinned by native defects. Similarities with results in layered metals such as NbSe2, in which defects nucleate halos of incipient charge density wave at temperatures above the ordering transition, raise the possibility that order–parameter fluctuations, but no static order, would be observed in the normal state of most cuprates if disorder were absent.

Ideal charge-density-wave order in the high-field state of superconducting YBCO

“…Although the proposed inhomogeneity picture qualitatively captures our experimental observations, it is not obvious that the Cu and O lines in NMR are readily interpreted as the sum of contributions from a unidirectional and a bidirectional CDW (4,6,21). We tentatively suggest that this reflects the fact that the local CDW correlations-to which NMR is most sensitive-are similar in the more-and less-disordered regions, and that it is only subtle, long-distance correlations that distinguish them.…”

“…Thus, the properties of the quasi-2D CDW are likely strongly affected by disorder and only indirectly represent the true nature of the underlying CDW correlations. Indeed, X-ray scattering shows that the onset of the quasi-2D order is gradual without a sharp transition (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), consistent with the influence of quenched disorder on an incommensurate CDW (19)(20)(21). Furthermore, whereas Y-based and La-based cuprates exhibit a clear competition between CDW and superconductivity (7,8,(12)(13)(14)(15), such competition is not apparent in the families of Bi-based and Hg-based cuprate compounds (9-11)-a discrepancy that probably reflects different degrees of quenched disorder among cuprate families.…”

Charge order from orbital-dependent coupling evidenced by NbSe2

“…In strongly coupled CDW materials, a pseudogap typically appears through the presence of locally fluctuating charge order without long-range coherence 23 . These same charge fluctuations have recently been suggested to play a central role in the description of the pseudogap phase of cuprate superconductors [25][26][27][28][29][30] . The precise nature of the pseudogap in these materials, however, is difficult to establish owing to the presence of various nearby competing orders.…”

“…The dynamical fluctuations in this regime may become locally pinned in the presence of defects, creating islands of order up to T ¼ T RPA E300 K, in agreement with recent STM and X-ray scattering experiments 23,24 . The properties of this regime are reminiscent of the features that characterize the pseudogap phase of cuprate high-temperature superconductors 35 , which have recently been shown typically to contain charge-ordered phases of their own [28][29][30] . Specific similarities are the presence of a pseudogap, Fermi surface arcs, dynamical fluctuations and a corresponding sensitivity to the timescales employed by experimental probes, as well as the existence of the crossover to the normal state at T* ¼ T RPA .…”

Broken rotational symmetry on the Fermi surface of a high-Tc superconductor

“…Broken C 4 symmetry is observed in a number of experiments on unconventional superconductors, including transport, 1-4 nuclear magnetic resonance (NMR), 5,6 neutron scattering, 7,8 X-ray scattering [9][10][11] and scanning tunneling microscopy. 12,13 In the iron-based superconductors broken C 4 symmetry is observed directly on the Fermi surface, 14 and has been taken as an indication that this broken symmetry drives the high T c .…”