Electrical Resistivity Anisotropy from Self-Organized One Dimensionality in High-Temperature Superconductors

Abstract

We investigate the manifestation of stripes in the in-plane resistivity anisotropy in untwinned single crystals of La2−xSrxCuO4 (x = 0.02-0.04) and YBa2Cu3Oy (y = 6.35-7.0). It is found that both systems show strongly temperature-dependent in-plane anisotropy in the lightly hole-doped region and that the anisotropy in YBa2Cu3Oy grows with decreasing y below ∼6.60 despite the decreasing orthorhombicity, which gives most direct evidence that electrons self-organize into a macroscopically anisotropic state. The transport is found to be easier along the direction of the spin stripes already reported, demonstrating that the stripes are intrinsically conducting in cuprates.PACS numbers: 74.25. Fy, 74.25.Dw, 74.20.Mn, 74.72.Dn, 74.72.Bk The mechanism of the high-temperature superconductivity is not settled 15 years after its discovery, mostly because it is unclear how best to describe the stronglycorrelated electrons in the high-T c cuprates. It has recently been discussed [1][2][3][4][5][6][7][8][9][10][11][12][13][14] that the electrons in cuprates self-organize into quasi-one-dimensional stripes, which might bring a paradigm shift in our way of understanding the two-dimensional (2D) electronic system in the cuprates. Though the self-organization is interesting in itself, the conventional wisdom suggests that the stripes are destructive to the superconductivity, because charge ordering would normally lead to an insulating state. However, there are intriguing theoretical proposals [10][11][12] that stripes can instead be responsible for the occurrence of the high-temperature superconductivity if they are conducting and meandering -properties that have never been clearly demonstrated before.In this Letter, we report novel in-plane transport anisotropy in the cuprates, which gives direct evidence for the conducting charge stripes in these materials; the temperature dependence and the magnitude of the anisotropy strongly suggest the stripes to be meandering and forming an electronic liquid crystal [11]. The evidence is shown for two representative materials of the high-temperature superconductors, La 2−x Sr x CuO 4 (LSCO) and YBa 2 Cu 3 O y (YBCO), highlighting the universality of the charge-stripe phenomenon in the cuprates. Most notably, the data for YBCO indicate that the charge stripes govern the transport in samples with T c of as high as 50 K, demonstrating that theories of high-temperature superconductivity should inevitably consider the self-organization of the electrons as an integral part.It is fair to say that the majority of the researchers today believe that the stripes are irrelevant to the superconductivity. This general belief comes not only from the conventional wisdom mentioned above but also from the current experimental situation, which can be summarized as follows: (i) strong evidence for the charge stripe order has been reported [1] only for Nd-doped LSCO, where the superconductivity is strongly suppressed; (ii) in other superconducting cuprates, evidence [2][3][4][5][6][7] is reasonably strong f...

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

“…The bidirectional phase can still be locally stripe-like (17), but with the orientation of the stripes determined by the local disorder potential rather than by the orthorhombicity. Indeed, a strong tendency to nematic order (oriented by the weak orthorhombicity of YBCO) has been inferred from various experiments (24)(25)(26). In SI Appendix we illustrate these points using an effective field theory and also address the cross over from 2D to 3D correlations at σc.…”

Quantum spin excitations through the metal-to-insulator crossover inYBa2Cu3O6+y

“…7(a) and 7(b)] suggest that these changes in spin dynamical properties are related with the MIC and its associated quantum phase transition. Since the oxygen concentration in YBCO is difficult to determine precisely, the relationship between T c 's and the oxygen contents differ slightly by different groups 28,29,30 . The oxygen contents in Figs.…”

“…7(f)] is inconsistent with the naïve picture of stripe correlations. If stripe correlations were to explain the observed spectra, something more exotic, for example the electronic nematic phase 42 , might be required to become important below the MIC for YBCO 28,29 . In fact, the transport measurements in YBCO by Ando et al 28 had found an increase in the resistivity anisotropy between the a and b directions with the decreasing doping attributed to the "striped" or electronic nematic phase.…”

“…If stripe correlations were to explain the observed spectra, something more exotic, for example the electronic nematic phase 42 , might be required to become important below the MIC for YBCO 28,29 . In fact, the transport measurements in YBCO by Ando et al 28 had found an increase in the resistivity anisotropy between the a and b directions with the decreasing doping attributed to the "striped" or electronic nematic phase. Ignoring the quoted oxygen concentrations as these may differ from group to group 29,30 , we find that the resistivity anisotropy becomes much smaller for samples with T c ≈ 50 K, consistent with our observation of isotropic spin excitations at low energies [ Fig.…”

“…The MIC happens in the underdoped regime for YBCO around y = 0.5 28,29 , while it occurs near optimal doping for LSCO ( x ∼ 0.16) 27 . If spin excitations are important in determining the charge transport properties of doped copper oxides, they might respond to the changes in the electronic correlations across the MIC.…”