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

Abstract

The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa 2 Cu 3 Ox (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (H c2 ) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO 2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to H c2 , given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an "ideal" disorder-free cuprate.high-temperature superconductors | charge-density-wave order | high magnetic field X-ray scattering | vestigial nematic order | competing order C harge-density-wave (CDW) order has been found to exist universally in the hole-doped superconducting cuprates (1-18), and the common characteristics at zero magnetic field include bidirectionality, quasi-2D and short-ranged correlations (7-17). More specifically, the CDW diffraction patterns are found in both directions of Cu-O bonds in the CuO2 plane (Fig. 1A), and the CDW correlation lengths parallel and perpendicular to the planes (i.e., along the a-or b-axes and the c axis) are less than ∼ 20 and ∼ 1 lattice constants, respectively (7-16), corresponding to a correlation volume of order 10 2 unit cells (UCs). 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 (7-17), consistent with the influence of quenched disorder on an incommensurate CDW (19-21). 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.Recently, a CDW with significantly longer correlation lengths was observed in superconducting YBCO (Fig. 1B) via X-ray scattering at high magnetic fields (13,14). This reveals the character (i.e., 3D) of the high-field charge ordering previously inferred by other measurements (3-6). At a magnetic field of ∼ 30 T, i...

Visualising the Charge and Cooper-Pair Density Waves in Cuprates

“…These high-field x-ray diffraction measurements also find that CDW-II is uni-directional, with modulations along only one of the Cu-O directions [55,56]. This is in agreement with earlier high magnetic field NMR measurements showing a splitting of 63 Cu lines for B > 28.5T, consistent with a uni-directional modulation of charge density along a Cu-O direction [57].…”

“…Interestingly the high field CDW observed in YBa 2 Cu 3 O 6+x appears to be completely unidirectional [55,56]. However, the orthorhombicity of YBa 2 Cu 3 O 6+x means that this is not a true breaking of rotational symmetry because the Cu-O directions were not equivalent to begin with.…”

“…Developments in high magnetic field x-ray diffraction techniques are providing exciting new information about the cuprate CDW [54][55][56]. Pulsed field measurements utilising a free electron laser have detected the onset of a CDW in YBa 2 Cu 3 O 6+x in applied magnetic fields 15 T, with a correlation volume of ∼ 10 5 unit cells.…”

“…Further weight is added to this by the observation in YBa 2 Cu 3 O 6+x , at B=30T, of a magnetic field induced CDW with a resolution limited in-plane correlation length ξ ≥ 230Å [56].…”

Spin susceptibility of charge-ordered YBa 2 Cu 3 O y across the upper critical field

“…The dispute has become particularly acute in the context of the competition between superconductivity and charge density wave (CDW) order recently revealed by nuclear magnetic resonance (NMR) [3][4][5], x-ray scattering [6][7][8][9][10][11][12][13] and sound velocity [14] experiments in underdoped YBa 2 Cu 3 O y . An interpretation of thermal conductivity experiments in high magnetic field H argues that H c2 becomes as low as ∼24 T for p 0.11 doping [15] (here p changes upon varying the oxygen content y and the relation between p and y is discussed in the Materials & methods section).…”