Anomalies in the Fermi Surface and Band Dispersion of Quasi-One-Dimensional CuO Chains in the High-Temperature Superconductor YBa_{2}Cu_{4}O_{8} (original) (raw)
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Physical Review B, 2012
We present magneto-transport calculations for YBa2Cu3O 7−δ (YBCO) materials to show that the electronlike metallic chain state gives both the negative Hall effect and in-plane anisotropic large Nernst signal. We show that the inevitable presence of the metallic 1D CuO chain layer lying between the CuO2 bilayers in YBCO renders an electron-like Fermi surface in the doping range as wide as p = 0.05 to overdoping. With underdoping, a pseudogap opening in the CuO2 state reduces its hole-carrier contribution, and therefore the net electron-like quasiparticles dominate the transport properties, and a negative Hall resistance commences. We also show that the observation of in-plane anisotropy in the Nernst signal-which was taken as a definite evidence of the electronic 'nematic' pseudogap phase-is naturally explained by including the 'quasi-uniaxial' metallic chain state. Finally, we comment on how the chain state can also lead to electron-like quantum oscillations.
Physical Review B, 2009
We use microprobe angle-resolved photoemission spectroscopy to study the Fermi surface and band dispersion of the CuO 2 planes in the high-temperature superconductor, YBa 2 Cu 4 O 8 . We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction ͑ ,0͒ than the b direction ͑0,͒, whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a nontrivial hybridization between the planes and chains. This asymmetry has an important implication for interpreting key properties of the Y-Ba-Cu-O family, especially the superconducting gap, transport, and results of inelastic neutron scattering.
Buried double CuO chains in YBa2Cu4O8 uncovered by nano-ARPES
Physical Review B, 2019
The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate systems by means of standard angle-resolved photoemission spectroscopy (ARPES); cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and the size of a typical beam results in ARPES signals that are superposed from both terminations. Here, we employ spatially-resolved ARPES with submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in YBa2Cu4O8. We present the first observation of sharp metallic dispersions and Fermi surfaces of the double CuO chains buried underneath the CuO2plane block on the BaO terminated surface. While the observed Fermi surfaces of the CuO chains are highly one-dimensional, the electrons in the CuO-chains do not undergo significant electron correlations and no signature of a Tomonaga-Luttinger liquid nor a marginal Fermi liquid is found. Our works represent an important experimental step toward understanding of the charge dynamics and provides a starting basis for modelling the high-Tc superconductivity in YBCO cuprate systems.
Pseudogap in the chain states of YBa 2 Cu 3 O 6.6
As established by scanning tunneling microscopy (STM), cleaved surfaces of the high-temperature superconductor YBa 2 Cu 3 O 7−δ develop charge-density wave (CDW) modulations in the one-dimensional (1D) CuO chains. At the same time, no signatures of the CDW have been reported in the spectral function of the chain band previously studied by photoemission. We use soft x-ray angle-resolved photoemission spectroscopy to detect a chain-derived surface band that had not been detected in previous work. The 2k F for the new surface band is found to be 0.55Å −1 , which matches the wave vector of the CDW observed in direct space by STM. This reveals the relevance of the Fermi-surface nesting for the formation of CDWs in the CuO chains in YBa 2 Cu 3 O 7−δ . In agreement with the short-range nature of the CDW order the newly detected surface band exhibits a pseudogap whose energy scale also corresponds to that observed by STM.
2005
We report the infrared (IR) response of Cu-O chains in the high-$T_{c}$ superconductor YBa$_{2}$Cu$_{3}$O$_{y}$ over the doping range spanning % y=6.28-6.75. We find evidence for a power law scaling at mid-IR frequencies consistent with predictions for Tomonaga-Luttinger liquid, thus supporting the notion of one-dimensional transport in the chains. We analyze the role of coupling to the CuO$_{2}$ planes in establishing metallicity and superconductivity in disordered chain fragments.
Physical Review Letters, 2007
We use microprobe Angle-Resolved Photoemission Spectroscopy (µARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. In the CuO2 planes, a two dimensional (2D) electronic structure with nearly momentum independent bilayer splitting is observed. The splitting energy is 150 meV at (π,0), almost 50% larger than in Bi2Sr2CaCu2O 8+δ and the electron scattering at the Fermi level in the bonding band is about 1.5 times stronger than in the antibonding band. The CuO chains have a quasi one dimensional (1D) electronic structure. We observe two 1D bands separated by ∼ 550meV: a conducting band and an insulating band with an energy gap of ∼240meV. We find that the conduction electrons are well confined within the planes and chains with a non-trivial hybridization. PACS numbers: 74.25.Jb, 74.72.Hs, 79.60.Bm
Renormalized band structure of CuO2 layers in superconducting compounds: A mean-field approach
Physical Review B, 1990
We have analyzed the band structure of a CuOz plane including two copper orbitals {d 2 2 and X d») and two oxygen orbitals {p", p~) in a tight-binding approximation. A Hubbard interaction between copper d holes has been considered with use of a slave-boson technique, while oxygen and copper holes interact via a nearest-neighbors Coulombic repulsion treated in the Hartree-Fock approximation. The resulting band structure opens the way to a comparison with the experiments and to some theoretical implications on the pairing mechanism of high-T, superconductors. The electronic structure of the high-temperature superconductors has been a controversial issue ever since their discovery by Bednorz and Muller. ' There is a general agreement in the scientific community in assigning a major role to the Cu02 layers in determining the normal and superconducting properties of these materials. At zero doping the Cu02 system has one hole per unit cell residing on Cu sites with d, 2(b,) symmetry. The additionx al holes introduced by doping in the superconducting samples reside on oxygen sites because of the large Hubbard repulsion on Cu sites Ud (of the order of 8-10 eV).
The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes of YBa2Cu3O6+x (YBCO) has been in focus for a long time. Although the CuO-chains are known to be important as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO, the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST) remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanar orbitals during the MST of optimally doped YBCO leads to substantial hole-transfer from the chains into the planes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transfer configurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXS spectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting state and, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. In the quest for understanding the fundamental mechanism for high-Tc-superconductivity (HTSC) in perovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens a unique novel channel for studying the dynamics of HTSC.
Coexistence of superconductivity and incoherence in quasi 1D chains
Arxiv preprint cond-mat/ …, 2006
The dimensionality of a correlated many-body system has a large impact on its electronic properties. When electrons are confined to one-dimensional chains of atoms their behavior is very different than in higher dimensional systems because they become strongly correlated, even in the case of vanishingly small interactions. The chains consisting of copper and oxygen atoms are particularly interesting, because the CuO orbitals are constituents of all known high temperature superconductors. Most of previous spectroscopic studies of CuO chain systems indicated insulating behavior[23-25]. Here we report the discovery of momentum dependent superconducting gap and hump-peak-dip structure in the spectra of the CuO chains. We demonstrate that superconductivity in the chains arises due to proximity effects and the peculiar momentum dependence of the superconducting gap shows how three dimensional coherence emerges in a layered superconductor.